In a moment of honesty I will admit I don't have strong evidence against the null hypothesis that my dislike of veganism and related is primarily due to their association with radical green movement, and New Age style fringe, both which I strongly dislike for quite rational reasons.

I can obviously say "meet is healthy", "humans are omnivores", and the ever popular "think of the children" (by the way if you haven't read Eliezer's Three World Collide, do it now, it's awesome) - but I think they're all rationalizations for my dislike I developed after being exposed to too many meat-avoiding freaks, and not primary reasons.