I don't know what AlexU meant by "sanctimonious twits"... Like others on this thread, I have not encountered evangelical vegetarians. In fact, a lot of vegetarians don't want to talk about it, for fear of getting criticized.

But consider what Emily said

I admire the vegans: not sure that I could ever manage that! But nor do I see much of an ethical impulse to.

A lot of why people are vegetarians is to be admired for doing something difficult. It's important that they have some kind of reason as an excuse for doing it--they can't admit to showing off--but it's impressive and admirable to people who think that it is pointless.