I don't think that the edit to this response [1] was ideal. If a response is incorrect, we can point that out in comments, or vote it down. But editing someone else's non-community-wiki answer should be limited to obvious typos, math fixes, and similar "invisible" fixes. This edit seems exactly like the sort of remark that should be in a comment.  Otherwise we will run into all sorts of "disagreements" over whether some proof is "correct". I would not appreciate someone editing one of *my* posts in this way, and I have much more more mathematical self-esteem than an a student or hobbyist would likely have. 

Added: I don't want to imply that the person who made the response is an amateur; his profile shows that he isn't. That's even more reason to let him fix his own answer and respond they way he likes. 

1: http://math.stackexchange.com/posts/4468/revisions