As a casual user of both sites, I have had pretty much only positive experiences. I use both sites are starting points for ideas not the final truth on a subject[1]. When one invests a lot of time into something, one usually becomes emotionally involved and that can lead to conflict in these massively collaborative projects. The only time I post to either site is when I am looking for an answer and can't find it -- if the question is not posted I'll post it myself or if I figure it out later I'll go back and post the answer (or edit the page in the case of Wikipedia). My usage is pretty sparse, but I have never experienced moderators lashing out at me in any unfair way.
[1]: Especially with Wikipedia I tend mainly to use it as an aggregation of links to other more trustworthy sources. With SO, I test the answer myself before blindly using it.
But anyone can bring this up on meta, if they have data, if they have examples, and lobby for change.
It's interesting how some sites manage to be strict and not horrible while other sites don't manage that so well.
I'm not sure how that culture is nurtured. Setting expectations is important - but you can't do that for all gajillion sites; and you can't do it after you've left.