It's not true at all.
The people who post on the forums are a very self-selecting group, seemingly with a higher proportion of people who display antisocial tendencies that get flagged by other players. I would venture that the vast majority of normal players have never been flagged, banned, or anything, but the minority of players who have tend to put the onus for their antisocial behaviors on others, citing "other people being offended" or "speech police."
Put another way, not everyone who plays the game knows how to be a person, and the forum is overrepresented by players who don't know how to be people :)
