A contradiction in environmentalism:

1. That statistics and evidence suggesting the many negative environmental impacts (externalities) of processes through which individual sentient animals are turned into food, are accurate or approach accuracy; that the U.N.'s report (and many others like it), which argue that "...raising chickens, turkeys, pigs, and other animals for food causes more greenhouse gas emissions than all the cars, trucks and other forms of transportation combined," and that the environmental impacts writ large of "farmed animals" is an ecological disaster, is correct. And, 
2. What happens to the environment matters, or is an issue that creates direct binding moral or prudent obligations on us...    

If you accept these two statements, on what grounds, moral or otherwise, can you refuse to consider changing what you eat for dinner?

Leaving aside what I believe to be the validity of the philosophy of animal rights, it's undeniable that we eat meat out of habit, not need: we like how nonhumans taste, there's no need to consume them. Indeed, many within the health community argue that a diet free of nonhumans secures an optimally minimum healthy life; in fact evidence supports the claim that a vegan diet is healthier than omnivorism. Therefore, as mere taste is trivial when considering what is reasonable to ask individuals to give up (or allow to evolve) when concerning issues as dire as global warming, it's odd that any person truly concerned about the environment would refuse to consider sacrificing the pleasure they get out of eating a pig. 

Further, assuming that some sacrifice is necessitated by the enormity of the environmental problems that confront our world (a sound assumption I believe), I'm wondering how any environmentalist can attempt to compel - through legislation, discourse, education, etc. -individuals (or nations, the "world community," etc.) to change their environmentally unfriendly habits, which of course requires sacrifice, if they themselves are not willing to even entertain the idea of changing those direct actions (i.e., eating meat, dairy, eggs) in their own lives that most degrade and harm the environment they seemingly aim to protect and defend.     

This is not the "blame game," I simply believe that we ought to be logically and morally consistent in our claims - a seemingly uncontroversial requirement that those environmentalist who refuse to go vegan, fail to recognize.

In the end, it's willpower, an effort greatly simplified because you know that you are doing the right thing. Veganism isn't crazy or radical, any more than driving a hybrid car, riding a bike, opening your window instead of using the air conditioner, or passing 'cap and trade' legislation is crazy or radical. It's aimed at the same end, and if you accept that end as legitimate or good, it's perfectly irrational - maybe even morally wrong - to do anything other than changing your eating habits. Nobody's perfect; however, this isn't difficult or obscure, simply don't purchase dead cows.   

Let me ground what I'm saying to better expose this contradiction (hypocrisy?):

This isn't some monumental effort to convince Washington of the necessity of 'cap and trade' legislation, or compelling the auto industry to increase fuel standards; this isn't like the devastating economic harm that a truck driver, for example, would suffer if we asked him to drive less; or the trauma of converting the U.S. energy infrastructure from fossil, nuclear, and coal to clean and renewable energy sources, etc. etc. It's as simple as using different light bulbs.

Indeed, I downplay the pyschological difficulties of giving up cows, chickens, turkeys, and pigs. However, as I've done just that and I'm certainly not so bold (or ignorant) to proclaim my extra-worldly or human-plus prowess and ability, it can be done when you allow yourself to accept that it is as a matter-of-fact the right thing to do.