I'm skeptical of this... I think it's because vegan-ism is so puritanical, and everyone hates puritans.

It would be different if 1) it was necessitated by a health concern, or 2) they were just people who tried to eat as few products made from commercial farming as possible, but would eat animal products as circumstances necessitate. But they cut out all animal products, to the point that it can be really really difficult to prepare food for them. And I understand that usually vegans try to be accommodating and just bring their own food; they aren't trying to be dicks to everyone. But they still forgo the aspect of social bonding created by preparing food for others and sharing food with others, which drives social distance between themselves and others on purely ideological grounds.