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Your main point is well taken ("Vegans who drive personal vehicles can shut their self-righteous yaps about global warming") and I agree with it, but only because of the "self-righteous yaps" part. The ideal solution to most problems is for everybody to "shut their self-righteous yaps" and instead engage in reasoned, honest discussion of the issues. So: does driving contribute to global warming? Yes. Does eating meat? Well, this article sure makes it sound like it does. So if our only overriding goal is reducing global warming, we should all refrain from both. But we have other concerns, one of which is convenience. And it is inconvenient to be vegan, just as it is inconvenient not to drive. But I don't see why either party would condemn the other. As I said in a previous post, doing a little is better than doing nothing, and anyone (from any side) who argues differently seems to be obviously wrong.
Also, a minor quibble. You pointed out that vegans tend to think meat is gross. I think that's probably true, but you say "it's not exactly a moral triumph that they abstain from it." I would put the arrow of causation the other way: it's not that it's gross therefore we stay away from it; it's that we stay away from it and therefore it's gross. Once you've gone a fair amount of time without eating meat, much of it does seem pretty gross. I mean, it is, after all, bloody muscle and flesh that came out of an animal. You have to admit that's kind of gross, right? If it was human flesh instead of animal flesh you'd think it was gross, but physically and aesthetically it's the same thing. I think the only reason most people don't find meat gross is because they grew up with it and are used to it.