Sure, I'll tackle that one head on.
It's not true. Almost all new members and forum participants manage to assimilate themselves into this community without crapping all over any and all social conventions and norms and are received hospitably.
When they don't, however, much as you've experienced, the community has a tendency to try to guide them towards more acceptable behaviour. When guidance proves ineffective, the tone changes, and understandably so. It's the same in any community, virtual or real.
* Blub *