I think this is an important point for people to accept, acknowledge, and keep in mind as a reason to strive harder to be open and accepting to people, especially those you don't agree with. I got a bunch of attacks from members of the open source community, due to developing my XML parser. ( Grant McLean and others ) I also got attacked by Poul-Henning Kamp, and then threatened that he would "shame" me for pointing…
The internet in general has problems with this, but I suspect it's much worse in the open source world where unmoderated forums are standard. If you look at the moderation tools available in something like mailman, they're very poor. It's just not been a priority for technical discussion forums at all. And the social convention is to leave forums largely unmoderated anyway, so it's easy to get into a downward spiral…
The key idea in an open community is organic moderation. The currently influential people in the community "bless" the threads with interesting ideas/ patches; they decide how much deviation from "civil" behavior they can put up with. In a good community, attention-seeking behavior would be condemned by the influential people in the community. The health of the community depends a lot on the initial contributors.
It's true that this kind of model scares of a lot of contributors, but it also attracts many others who would have been eliminated in a pre-selection.
The main takeaway from Lennart's post is that more community building work is required: they don't automatically become good communities.