Agreeing to disagree is just as important in online discussion as in academic discourse and polite conversation, although it is more commonly overlooked.
Not everyone is able to agree to disagree. It can be seen as a weakness because it means accepting that you are in fact powerlessness to convince someone else. Not everyone can give up, especially if the conflict is about something they feel strongly about: You can not agree to disagree if you hate that person for their views.
Agreeing to disagree in the end means no more then putting the relationships you have before the conflict. Both sides need to care more about their relationship than about the subject of conflict; Online this can be too much to expect from people.
In agreement and disagreement it's important to separate facts and opinions. People should be able to agree on the facts. Disagreement is natural on opinions, interpretations, predictions, theories or speculations.
Conflicts often start when people try to sell opinions as facts, knowledge or truth. Sometimes people are even in good faith, not aware that they don't know exactly about their position in the intellectual jungle. Only when "What are the facts?" and "What do I believe?" are correctly answered, you can start to move out of this jungle.
The wiki separation of dissertation and discussion is an implementation of this separation of facts and opinions. The process of separation can be done in a consensual way, without conflict. This is part of the WikiWay. Dissertation and discussion seems a good basis for an AgreeToDisagree, if necessary.