A key part of this trust and respect is vulnerability. While it may take time to develop a level of comfort that allows one to become vulnerable, it is usually important to a community's health that participants have a degree of personal investment of self in the community. To some extent, a community may not even truly value a contribution if it doesn't have the full force of an "I believe this!" standing behind it.
While in society we expect everyone to present some VulnerabilityToCommunity (for a nearly ridiculous extreme example, bulletproof vests are illegal), we could not achieve this if we disrespected it. The CommunityExpectation is that everyone here is vulnerable in some way or another. The community must DefendEachOther as a result, and certainly we should not engage in VigilanteJustice to exploit this vulnerability. We have gun control because bulletproof vests are illegal because we don't want shoot outs when taking in a criminal. In an OnlineCommunity, particularly a wiki where all our words and reputation are open to editing, we must treat everyone with grace, charity, and respect in return for them joining the community respectfully and with grace. Harsh criticisms, particularly ad hominems, but also abusive roles such as RecordKeepers and trolls are not tolerable. Many community theorists in sociology actually think both personal investment (ConnectionToCommunity??) and vulnerability are necessary to define a community.The vulnerability of being left out in the cold may be sufficient in small cases rather than requiring any other forms of vulnerability, although some form of PeerPressure is also necessary.
On MeatBall, obviously, people who wish to use a name are expected to use their real name, increasing their vulnerability to the community, even though this is a CommunityOfGlassHouses and you are really becoming vulnerable to everyone on the InterNet when you become vulnerable to MeatBall. Anonymous contributors are unknown, and therefore are voluntary outsiders, even if to PostAnonymously is a fair and reasonable choice since we accept anonymous contributions offered civilly and in good faith. That said, usually the name alone will not incur a lot of vulnerability: It won't be linked to any real person or other OnlineIdentity, unless you do that yourself. On the other hand, there's really no true anonymity or even pseudonymity on the InterNet these days, so the difference between giving a real name and giving a false one is not really that significant to the InterNet at large - if someone wants to find your words, they'll find them.
Anonymous voices are considered with integrity and respect (cf. FairProcess). Anonymous contributors can't use a tactic like threatening to leave to force an issue. They can only teach us. As a result, the best decisions here are made completely anonymously.
People are vulnerable in online communities in many different ways, not all having to do with using real names, but this is an important piece of MeatBall culture, oft-discussed.
The use of RealNames implies a certain amount of personal investment and vulnerability. Use of pseudonyms breaks this public trust. This leads to the suspicion that either the participant does not trust the community, or that the participant is not themselves trustable. We want to get to know participants for who they are, not some image. It helps us when working together, raising barns, etc. to deal with people for who they really are. That's one reason why some of us keep an OnlineDiary. Since we have no face-to-face meetings, it's difficult to build a team (vs. a group) due to the lack of socialized ParaLanguage. But if you fake it all through a pseudonym, it'll be difficult to work with you.
Attempts to avoid vulnerability through using a pseudonym or remaining anonymous can backfire. Still, anonymous contributions are accepted on MeatBall - see point 2 of UseRealNames - although you certainly can't participate in TheCollective or be a substantial part of serious decision-making in any community while remaining anonymous. (But on the other hand, think about the SecretBallot? used in many voting processes in other communities...)
See also: SemanticsOfIdentity, IdentityValidation, EnforceResponsibility, PenName, BasisForPseudonymity, FocusOnIdentity, ImportanceOfIdentityInOnlineCommunities.