I didn't read the whole thing, but it's kind of a religious mindset to me. Because Paleo types actually think carefully about their food, they are supposed to come to the "right" conclusion -> vegan. It's like knowing and then openly rejecting the religion you grew up with (apostasy)- much worse than not ever hearing / caring about it. It's all about emotion and ingroup / outgroup dynamics. Come to think of it, the hate on vegans from paleos is pretty much the same thing.
If you are new to the PB - please ignore ALL of this stuff, until you've read the book, or at least http://www.marksdailyapple.com/primal-blueprint-101/ and this (personal fave): http://www.archevore.com/get-started/