I steer clear of such communities, unless I need to extract some specific bit of information out of them (and I leave immediately when I'm done). Perhaps that's because in my upbringing calling someone a fool (let alone a retard) was considered extremely rude.

If you can't call a retard a retard

Do you know the person you're calling a retard well enough, our you're judging by a couple of their posts? Would you say "you are a retard" to their face in real life? When you call someone a retard, what do you imply, "your mental abilities in general are very poor" or "you are incompetent at activity X which we discuss here"?