"I've asked this a couple times in this thread: why is animal, human-like life more deserving of respects and rights than plant life? Note that any answer that refers to 'thinking', 'feeling' and 'suffering' implicitly uses human life as the standard for what is valuable, and is thus the same form of reasoning a meat-eater uses to justify eating animals other than humans."
As an error theorist (or nihilist), I'm pretty sympathetic to the claim that all moral norms are necessarily arbitrary. Be that as it may, people generally grasp for reasons to explain why it's wrong to harm people. The simplest and most common explanation is of the following sort: suffering is intrinsically bad, and we're obligated to avoid causing evil in the absence of morally significant countervailing considerations. Why bring race or species into the explanation? I don't think the answer is that we end up with moral principles that are more intuitively appealing upon due and impartial reflection. Rather, doing so allows us to justify patterns of exploitation and domination that many of us find prudentially agreeable.
The idea of rights for plants is every bit as queer as the notion of rights for rocks. Neither group has any use for them.
-- Luke