You assume that we want to abolish any form of racism/discrimination of other life forms. You say that we now draw the line between humans and animals. What if we draw the line between human-animals and plants? How can we be certain of a plants faculties? They also have purposeful behavior. A bit of discrimination is necesarry.
And your arguments are based on the belief that we have absolute objective morality. I believe that morality is relative. I could've believed in it too, but real life is different. We arent pure creatures of reason, and therefore we cannot rely on reason to make all our decisions. As you said; you love your steaks even if you can argue quite well from a vegetarian point of view.
In my personal opinion I think many of the great philosophers have proved themselves wrong with the passing of time. Plato, Sokrates and Aristotle all believed in objective morallity, yet they all believed that women were inferior to men. They were radical in their time, and if they lived today they would all have a different view. That just shows how morallity will adjust to the time you're living in, and therefore there cannot be a absolutely objective morallity.
Oh, and I suppose I broke a taboo when I posted before I read the entire thread.
My apologies if I repeated someone elses arguments.