The reasons for our moral schizophrenia about non-humans are, of course, as complicated as the concrete manisfestations of our conflicting attitudes. Some of the reasons are historical alone; we have been exploiting animals for so long that we simply continue doing so by force of habit alone. Some reasons are rooted in culture and religion; we uncritically subscribe to various belief systems that proclaim humans (or some subset thereof, such as white males) as "superior" and to devalue non-humans. Some reasons are economic; animal exploitation is a billion-dollar industry - and human beings appear to be able to justify most actions that result in monetary gain.
And it goes on for several pages.... This was written by abolitionist Professor Francione. He is, for the lack of a better word, fucking amazing. I have read so much of his stuff since going vegan and I have never realized just how deep a hole we've dug ourselves in and the animals are paying for all of it.