Information is power, and reputation is VulnerabilityToCommunity. Often people do stupid things or regretful things that they would like others to ForgiveAndForget. However, some people refuse to forgive, and thus they refuse to forget. Online, this creates different problems than offline as digital content is subject to easy copying, storage, and republishing (cf. MarshallMcLuhan's publicy, MichelFoucault?'s panopticon, DavidBrin's TheTransparentSociety). DefensiveCopyright tries to provide a legal tool to limit people from doing this, but this isn't very effective. Ethics and social interaction provide a stronger tool that limits people from doing this without permission. That is, if you copy my text and I don't want you to, my anger will normally make you stop, lest you end any constructive relationship by your actions.
There is much to be angry about copied text. Since online discourse is LifeInText, everything we do or say is recorded digitally to be reproduced. FlameWars encourage people to do stupid things, like all fights: people will say things they don't mean, or do things they regret. People make mistakes. They may unwittingly publish personal information, make jokes muddy out of context, or deceive--advertently or inadvertently. Since we all have VulnerabilityToCommunity, our reputations are at stake. Copying text is PunishReputation as takes away our control over our lives (in text). We can no longer ForgiveAndForgetInSoftware, and thus we must restrain what we say, and that means we must restrain what we think as that is what LifeInText means.
This vulnerability and the anger associated with it provide the social levers of power that some enjoy. The text copied is often only that which is selectively chosen to be most vicious.
For instance, out of anger, one person in a flame war may decide to thwart ForgiveAndForgetInSoftware by maintaining a "permanent record" of the war to PunishReputation of his interlocutor; i.e. to embarass or to otherwise hold the person to account. However, flame wars are rarely so serious that they need such a heavy instrument to prevent the misunderstanding from occuring again. In fact, the heavy instrument will only exacerbate the conflict. Even if the FlameWar is resolved, people forget that they stored a copy of the discussion somewhere publically. If so, the flame war may reignite once someone else discovers this text, say a third party who tries to hold someone to account (even during another flame war), or even one of the RecordKeeper's opponents who discover the record. Thus, the semi-random and unofficial records of the RecordKeeper frustrate ForgiveAndForgetInWetware in a way that at least a full VersionHistory would not (i.e. AvoidIllusion of "forgetting.").
In another case, many will copy text of the "leaders" (structural, social) of an OnlineCommunity to "hold them to account," which may be valid if the leaders have any real power over them. But this can only be successful if the leader must work with the RecordKeeper; otherwise, it destroys the trust that is necessary to collaborate (cf. BarnRaising) between the two. Leaders may find the only option is to exercise their own RightToLeave (i.e. retreat) in order to protect their reputations and their time in defending themselves.
Conversely, leaders may hold copied text of their subordinates as blackmail to thwart the RightToLeave or to control the repurcussions of those who have exercised their RightToLeave. This is doubly evil if the leader is the GodKing with the power to bend reality; i.e. modify the records in public trust whilst maintaining a published yet privately held record.
Some RecordKeepers? are very dangerous, as they enter discussions with the intent to harm. Some argue that technical ability excuses social culpability, perhaps as flak for their subvertive practices. They have no respect for others in the discussion. They aren't interested in BarnRaising, but only in winning the argument. They are more likely to take an argumentative approach because they perceive that they have power over the other participants, and thus they can afford to enter discussions cocksure and fists up. They destroy ForgiveAndForget, often reversing the charge that the rest of the community does not ForgiveAndForget. They undermine the CommunityExpectations that allow the otherwise peaceable, fun interactions to continue. They do this because they think they can get away with it, and because they may even enjoy the sense of power they gain from it. While they might just be immature (cf. WhatIsaTroll), you may encounter a RecordKeeper with an actual personality disorder sometime in your travels online.  
It's critical to remember that most online discourse is not of the calibre that needs to be protected and archived. Yet RecordKeepers take the discussion much more seriously than others; that imbalance of intention will create serious communication conflicts in the future. In extreme cases, it may be necessary to question whether the RecordKeeper has a meaningful perception of the purpose of the discussion.
Therefore, remove the source of the RecordKeepers power. The RecordKeeper's power comes from two sources. First, factual, as he or she stores more information than others. Second, socially, as the information is only damaging to the potential victims given the wider social context they are embedded in; i.e. through embarassment/blackmail.
Regarding the factual sphere, one can level the technical field by abandoning ForgiveAndForgetInSoftware and keeping a full VersionHistory yourself. Now they are part of the same CommunityOfGlassHouses as everyone else, and there we AvoidIllusion that the digital sphere is safe. Be careful though if the community has a GodKing with the power to modify the history. The next level of warfare is to claim my (secretly edited) copy is the true version and the VersionHistory is a forgery. While 90% of people may know the truth, this attack on the community's integrity may be incredibly painful, especially as it implies not only some social injustice (i.e the content of the copied text) but also technical injustice.
Alternatively, you can work within a GatedCommunity where interaction is limited to trusted individuals who have put up collateral such as signing contracts (cf. DefensiveCopyright) or posting financial bonds to ensure their continued trustworthiness. This later concept isn't so far fetched as this is what companies do to protect their intellectual property from being published by employees.
Another possible option is to sue the person using your copyright, but the damage to the community or to you has to be pretty serious. If you have a CopyLeft or OpenContent license, you lose this privilege. You may even create inadvertent RecordKeepers when people download the tarball (copy the site), FlameWars, mistakes, and all.
Regarding the social sphere, the first measure is not publish any information of value. (cf. LimitTemptation) However, as OnlineCommunities tend to become LifeInText, this is not always possible. Instead, the community can EnforceResponsibility. Once a RecordKeeper is discovered, CommunityExile them. After all, the more emotionally involved they are with the community, the more arguments they will be a part of, the more text they will copy, the more blackmailed the community will be.
However, to effect the exile, you will naturally have to make a record that the person is a RecordKeeper. They may respond that you are violating ForgiveAndForget yourself, especially if they argue for their own amusement. This is true. We presume the person may have in fact made a mistake that they will never repeat. So, instead, make sure the record is time-limited. A very good time limit is "Exiled until the records are destroyed." That is a completely fair and balanced sentence, and it leaves room for them to return, and also exile them if they ever do it again.
Enforcing responsibility is usually a relationship ending move, and it may create more animosity than it resolves when applied to a person who is just pissed or is unaware of the philosophical and ethical issues surrounding the merger of the public and private spheres. Thus, if you are experiencing the wrong end of a RecordKeeper, the community must at least realize that the person is quoting from context long and best forgotten. This puts the victims of the RecordKeeper on an unfair footing. If it has been a long time and the issue was otherwise dead, the community must come together against the RecordKeeper. It's important that everyone does this as there might be another legalistic individual in the crowd that will also try holding the victim to account because she believes past behaviour is definitive of current or future behaviour. This may cause a chain reaction. Try at least to explain that record keeping is unappreciated and that you refuse to respond to it. Treat it like "inadmissable evidence." It's hard, but no harder than ForgiveAndForgetInWetware.
But, keeping records is the standard advice to defend against bullies who use SnipingCriticism and similar perpetual low level attacks. Keeping records can also be a rather important defence if you've inadvertantly contributed to a community where the resident GodKing has the power to transparently rewrite history to make themselves look better, and their critics looks worse, without any kind of AuditTrail or other limits on that power, such as HitchHikersGuideToTheGalaxy. Nonetheless, keeping records for an OnlineCommunity may be more trouble than its worth. If you suffer under bad GodKings, exercise your RightToLeave rather than spend your life fighting for your reputation. If you suffer bullies, use the number of other ConflictResolution and DissuadeInteraction patterns to get rid of them. If you have to fight, say if you are defending an institution like IndyMedia, good luck.
Interesting discussion. A third approach that I think it'd be interesting to consider (and that, I admit, seems to me to be the correct one) is to acknowledge that there will often be record keepers, and that there will always be the possibility of record keepers, and to just get used to it; deal with it by developing habits and solutions and institutions that are robust to the presence of record keepers.
Why get used to it? Because (at least in the kinds of communities we're mostly talking about) record keeping is cheap and easy, is often desirable for reasons other than for use in conflicts (in fact I'd claim that it's usually done for other reasons), and is sometimes even automatic; and because none of the countermeasures actually work (license and copyright don't work in practice unless the record keeper attempts to profit financially from his records (CopyrightDoesntMatter), social pressure doesn't work against people who don't tell anyone about their records or against people who don't care (any longer) about the opinion of the community, etc).
How get used to it? As more and more people take part in LifeInText, the fact that someone said something dumb in a flamewar three years ago will become less and less surprising or important to anyone. Perhaps keeping in mind that anything I say can be recorded for eternity will encourage people to think a little harder about what they say. Perhaps the awareness of record keeping will incent us to develop useful methods of anonymity and pseudonymity that will give people space to say things that they don't want attached to them forever. Perhaps we can find ways to do ForgiveAndForget even if a record exists; the two aren't necessarily incompatible (it's possible to say, "oh, yeah, but that's water under the bridge, that's forgotten", even if a digital copy of it still exists).
Trying to prevent record keeping is probably a losing battle in the long run. This doesn't mean there's no use in fighting a rearguard action in the short to medium term. But in the long run, I'd suggest we at least consider what it'd be like to just bite that bullet, and get used to it.