What's up with all of the vegan hating?

Today I, once again, made the mistake of reading a post on the Freakonomics blog and then reading engaging in the comment section.  This post was kind of about biking and veganism and their relative environmental merits, though in many ways it wasn't really much of a post or all that much about either of these topics.

Despite the fact that there really wasn't all that much meat in the post itself, quite a number of commenters latched on to the vegan thing and ran with it.  And with their cause in hand they ran right to the land of criticism.

While reading the comments I learned,

It’s a moral choice because Vegan foods are almost always [sic] awful than foods that actually cater to human biology and evolutionary preferences.

and that 

Biking is fun. Eating vegan not so much. 

Maybe these aren't the most anti-vegan comments that are out there, but, at least as far as I am concerned, they pretty obviously incorrect.  I would guess that most foods people eat on a daily basis are already animal product free.  Maybe more importantly, I would guess that most people quite like many of the vegan foods they enjoy on a daily basis.  Furthermore, many vegan foods are pretty straight forward to make/acquire and are pretty tasty.

The other part of the equation that I don't quite understand is the apparent indignation that many people exhibit when they hear about the idea of a vegan diet.  Does it really make sense to be upset that someone else has decided not to eat any animal products?  Especially in the US context where 'freedom' is a cause célèbre, why should it matter if some one has decided not to eat meat for for whatever reason?

A related issue that I find similarly frustrating is the suggestion that humans have evolved to eat meat and therefore should eat meat.  Unfortunately, for better or worse, despite that the fact that most humans share many traits, it is not the case that all humans react the same way to all foods.  It's pretty clear that quite a large portion of the population doesn't respond well to dairy products, and there are other portions of the population that don't respond well to other foods - some people even have a hard time with meat.  So in those cases when the consumption of particular animal products may cause illness or discomfort it seems reasonable that they should be avoided.

But this also demonstrates that a uniform human diet isn't feasible or desirable.  Promoting the misconception that all humans need to consume meat and/or dairy is likely to lead to adverse effects in some portion of the population.  By denying the fact that humans are different and that they may respond to foods differently we risk discouraging individuals from becoming aware of the fact that the consumption of certain foods may be having negative impacts on their health.