Forum Moderators: not2easy
If you do edit a post, I think it's a good idea to make sure you aren't changing the sense of the post. If your edits are so significant that the poster might feel his point is lost, it might be better to delete it.
I would reject the entire message as not being appropriate because it doesn't meet the charter or acceptable levels of the forum and state why you are rejecting it: allow the poster to make adjustments and resubmit.
Keeping a history of changes is probably not good enough - the fact is that you're editing it. If this is how you want the nature of your forums to be, then you probably need to make it explicit in the TOS (as mentioned above).
I think it also puts you in a dubious legal situation because now you are a co-author of the message, and taking some of the responsibility. Say the message results in a legal case (e.g. someone wants to sue the poster because the message alleges something defamatory), then the poster could claim they didn't write the defamatory part of it, you did because you edit the posts. And even if you make it clear what you have been editing, the poster may then try to stick it on you by saying that you somehow personally authorised the message, and so are in some way liable. Of course, if you have your TOS set up correctly, then none of this can happen :-). I don't know exactly how realistic this scenario is, but my point is that it seems like not the safest way to play the game.
As for editing beyond censorship, the author (not you) owns the copyright to his words. So, you need his permission to change it. I guess you could insert a condition into your TOS where posters agree to your editorial changes for anything they submit. However, I've read cases here where judges have ruled passive TOS' are not considered legally binding contracts. Visitors must actively acknowledge someway that they've read it.
That is correct.
There should be a "click-wrap" agreement. The way to do this is to make users register once (even if only with username and password) to be part of the forum, and include the TOS as an explicit agreement in that process. Then with posts to the forum, provide a clear statement that makes the poster aware of the original TOS that they agreed to.
This site is a good example of how to do it.
Legal cases can hinge on these issues, so it is very important to get it right.