"I have noticed that the naturalist fallacy is abundant in conversations about animal rights and vegetarianism."

Yep, any apologist for vegetarianism bumps up against it constantly. But it's not limited to this debate, by any means. Campaign against extreme poverty runs into "The poor will always be with us" thinking (thank you, Jesus and Deuteronomy), which is really just "the poor have always been with us," so the naturalist fallacy again. Of course, John Lennon's assault on the fallacy was inadequate, "you may say that I'm a dreamer, but like, let's suddenly start doing shit way different!" You've got to pay close attention to why things have unfolded the way have, and how/why/whether the pattern can be altered. In the case of both vegetarianism and extreme poverty, though, I think there's lots of evidence that change is very much within reach.