"Saying "I'm not against this idea, but it will make us extinct if we don't get rid of it" is meaningless to the point of hypocrisy - I can think of few clearer ways of stating that one is against something."
I know what you mean, and hopefully I can explain what Quinn means.
Firstly, he doesn't speak from a metaphysical point of view, he speaks from a pragmatic one.
When he says he's not "against" (his quotes) the idea that
humanity belongs to a separate and higher order of being he's showing his usual moral neutrality to unscientific myth of all kinds. Instead of going ad hominem on the the purely abstract idea, he's pointing out the real & present results of how that idea is being played out by a culture that is Conquering the Globe and All Life On It powered and directed by the myth that
humanity belongs to a separate and higher order of being.
I'm sure it's not lost on Quinn that there are multitudes at the extreme who deeply believe that hastening the end of the world is
literally a divine task. For "chosen" or "saved" humans only, of course.
"Intellectually, and hence in all sorts of important ways, human are far more different from dolphins or chimpanzees than dolphins or chimpanzees are from bacteria
I'd argue with that if it was more related to the point at hand. Even if we assume your statement is true, it doesn't logically follow that "man belongs to an order of being that is separate from and higher than the rest of the living community".
- we have the capacity of abstract thought, something no other species has even slightly
That's not true, but still wouldn't add up to "man belongs to an order of being that is separate from and higher than the rest of the living community". We can talk about dolphins and chimpanzees another time.
I'm curious about something. When and how do you think humans became human?