I wouldn't expect PETA to stop with their off-putting campaigns ("Your Mommy Kill Animals"), it is what they genuinely believe, and for them keeping silent and advocating "a healthier lifestyle" would be so far from their viewpoint that it would practically be a lie, even if it might win them more friends and influence.

Same with RMS. His views are radical, and toning his messages to make them more palatable down would be dishonest to who he is. Let someone else play the moderate and practical.

Of course, moderate and practical people don't dedicate their life to a message, be it "a healthier lifestyle" or "a better way to develop software". The Open Source spokespeople like Michael Tiemann or Tim O'Reilly) tend to get distracted by having a life to live.

Peter Singer argues against the species-ist argument that they're incomparable. Or that killing any human is worse than killing any (or even all) animals, i.e. he argues that for some human,animal pairs killing the human is less-worse than killing the animal.

http://www.princeton.edu/~psinger/faq.html :

> Q. I’ve read that you think humans and animals are equal. Do you really believe that a human being is no more valuable than an animal?

> A. I argued in the opening chapter of Animal Liberation that humans and animals are equal in the sense that the fact that a being is human does not mean that we should give the interests of that being preference over the similar interests of other beings. That would be speciesism, and wrong for the same reasons that racism and sexism are wrong. Pain is equally bad, if it is felt by a human being or a mouse. We should treat beings as individuals, rather than as members of a species. But that doesn’t mean that all individuals are equally valuable – see my answer to the next question for more details.

There is even vast common ground between meat eaters and vegetarians. Most people agree that killing primates it morally clearly wrong.

> Most people agree that killing primates it morally clearly wrong.

Roughly, you're probably right: killing primates is generally wrong. But it's not always, clearly wrong: killing a primate that's about to kill you, killing primates that are consistently killing other primates, killing one primate to save a hundred other primates, etc., etc. Singer's framework gives us a way to reason-through cases where there isn't consensus.

Within the group, you'll likely find a small subset that actually thinks meat is akin to human murder, but that takes a leap of logic that many vegetarians aren't willing to take when there are so many other perfectly reasonable reasons to choose the vegetarian lifestyle.

Nothing wrong with that and the letter makes that pretty clear. It's about persuasion and spot on when it comes to that.