Speciesism

In response to Andrew (here) and Sean (here)

Speciesism is characterized by assigning different rights and value to different species of animals based on morally irrelevant differences. Saying that humans are, in general, more valuable than dogs because humans have higher mental capacities is not speciesist. Saying that humans are better than dogs because humans walk on two legs, or rather, simply because they are human is speciesist.

A related problem, as you pointed out, involves not recognizing that there are no abilities that all humans have that most animals do not have; it's not speciesist, it's just factually inaccurate. The argument from marginal cases brings this particular point out. It would, I think, be speciesist to say that sentience only matter when it is possessed to the extent that humans have and that anything less than that is useless or irrelevant, because it involves arbitrarily assigning a point of relevance based on species.

I don't know if that helps any. I certainly think that most human lives are worth more than most animals lives, and I don't think that's speciesist.