For the unpersuaded, James McWilliams has a good post on the irrelevance of "potential" for certain qualities to moral status.
One of my hobbies is spending time in the philosophy sections of obscure book stores, looking for books that address animal ethics, and seeing what creative lengths people go to in order to justify speciesism. There are, of course, the religious arguments. Some of these are worth engaging, insofar as many people are open to moral discussion and secular reasons translate easily enough into religious ones (given the right interlocutor). But often people just use religion to dig their heals in about speciesism. Once you've started quoting scripture, you've lost me.
I once read something in defense of speciesism along the lines of, "You don't get it, it's a matter of kind." As if italics somehow make the point. "Kind" is just another word for species. And speciesism is just another form of prejudice.