That's the one thing I found with Killing Floor overall, the community was generally really pleasant and a pleasure to play with. Like most games of course you run into an arsehole at least a few times but compared to the acidic pit that is Left 4 Dead I never had many problems on Killing Floor servers. I admittedly tended to play on Normal/Hard servers and not really Hell On Earth so I'm not sure if it was any different on those servers.
Suicidal/Hell on Earth had great communities too. I had some great times playing those modes with randoms. In general assholes were kicked on sight.