I feel like a lot of the Dota/HoN/LoL or any esport gaming community pubs have never played a real-life team sport before competitively.
It's the anonymity, doesn't matter if you play sports for a living when you can call people out without any penalty. It doesn't work face to face, even at LANs progamers seem to behave. Though it's quite possible the ragers never make it to that level in the first place.