"The question is -- and this is what Barack Obama didn't want to answer: Is that human life a person under the Constitution? And Barack Obama says no," Santorum says in the interview, which was first picked up by CBN's David Brody. "Well if that person, human life is not a person, then, I find it almost remarkable for a black man to say, 'We are going to decide who are people and who are not people.'"Then what's a black man supposed to do? Nobody of any race can go through life without drawing the people / nonpeople distinction somewhere. For example, unless you draw it in such a way that some foods aren't people, you can't eat anything without committing a murderous act of cannibalism. And if your pants are people, you go around wearing people a lot, which is less bad but still kind of weird. The more serious disagreement involves animals -- some of us think they deserve some portion of the regard that persons do. Others don't think so.
The philosophical issue surrounding the personhood of the fetus is that some of us think you need a mind of some minimal sort in order to be a person, while others think it's just a matter of having human DNA, or being able to at some future point become a human. A few years ago I wrote something about why the former view is a lot better than the latter.
I'm not going to pretend that the psychological roots of people's feelings about abortion lie entirely in this philosophical question -- attitudes toward female sexuality play a huge role. But as far as the personhood question goes, drawing the person/nonperson boundary is something both sides have to do, and anti-abortion people shouldn't be taken seriously when they claim that only their opponents are doing it.