I was asked this question on a forum I visit. Since I haven't posted anything in a while, I figured I'd post my reply here, just in case anyone is searching for any reasons as to why they should be pro-choice instead of anti-choice.
I think it mostly has to do with the fact that I think women are human people capable of being treated like people who can make their own moral decisions rather than children who must be monitored and told what to do "for their own good". I don't think women should have to be forced to donate their bodily resources when no man is ever forced to. I don't think rape victims should be treated worse than their rapists just because they happen to have a uterus. I don't think women should be punished for enjoying or having sex, and yes, that goes for non-procreational sex. I'm not worried about the human race becoming endangered or extinct nor am I worried about poor infertile people not having any spawn, and I'm certainly not willing to subject women to uterine slavery to make sure they can have the white/male/healthy baby they're so desperately searching for while they "ZOMG would love to have any baby!1". I don't think it's fair to compare a woman and a fetus. They're not on the same level. A woman is a sentient human being. She is not potential. She is physically independent. I do not believe in magical invisible sex contracts that make women responsible for carrying any and every pregnancy by virtue of having a uterus and the need to have sex. Because yes, it is a biological drive, even for us women. I've read the stories of death-bed confessions and clandestine abortions not only from this country in the pre-Roe era, but also from other countries where abortion is still illegal. I see no reason why we should subject women to that for other people's fantasies of fetal personhood. I am a feminist and I care about women. I know that they are individuals with individual beliefs, situations, goals, bodies, and wants. I realize that being anti-choice in any situation creates a harmful hierarchy among women and especially between women and their doctors. There is no way to successfully implement exceptions, and I'm not willing to gamble with women's lives to protect the egos and misogynistic, out-dated traditions of patriarchy and those who would seek to uphold it whether consciously or not. Women have a right to make their own reproductive choices. If they want to be childfree, they should not have to be celibate until menopause. It's ridiculous to expect and it's misogynistic to implement. If they want to have 12 children, they should be able to choose to do so. The fact of the matter is, women should be treated like the people they are, and that requires trusting them enough to be able to make their own decisions.
So there you have it folks. Take your pick of the reasons. There certainly are many.