Indeed (well, worse actually, sentience). In a purely technical point of view you'd be right. But in our society we've always distinguished between non-human animals and humans. We care more for our own race. So within our culture it's common to treat them different. I often admitted that this is an emotional, irrational input in my choice.
But the decider here really is, has the foetus developed the beginnings of what defines us as human beings. And as human beings, and in the culture I live in human beings are valued far more than animals. And I actually do believe that one could make a very good argument that given the alternatives, it should be illegal to kill animals even for food.
I just happen to be that much of a bastard that I care more about the pleasure of eating a steak, but I'm not that much of a bastard that I support killing a human being who has the same or even a lower level of sentience. It's an emotional, irrational fault in my reasoning.