I agree that people should not need an (especially) thick skin to participate on Server Fault -- We should strive to be a welcoming place for all competent professionals that fit our target audience (obligatory reference to pretty chartobligatory reference to pretty chart).
In regard to comportment, the general rule for the main site (http://serverfault.com) is that it's the site's "office". You are expected to conduct yourself with a level of professionalism appropriate to a corporate/office environment with customers walking around, and we expect that participants on the site will treat each other with the same respect as they would a colleague.
Basically that means you can't swear, insult people's parentage, or call people names, and we expect that if you're going to answer the question your answer have the intent to help constructively resolve the problem being described (e.g. we have an absolute zero-tolerance policy for "destructive pranks" like posting rm -rf /*
as an answer - that's a bannin').
It does not mean that we are obligated to be obsequious buffoons and try to help everyone no matter how poorly constructed their question, nor does it mean telling someone "You're doing it Wrong!", "Don't do that!", or "This is a stupid idea!" is verboten - telling people when we think they're wrong is important, otherwise they keep doing bad things.
We shouldn't be deliberately mean when telling someone they're Doing It Wrong, but neither should we pull punches to spare their feelings at the expense of their professional competence (or worse, their production environment's stability) -- As professionals we have an obligation to point out when someone is doing something bad, and to advise them not to do so.