People opposed to the right to get an abortion like to make the argument that a fetus is alive, has a heartbeat, can feel pain, etc. It's obvious that these features are not sufficient to make the case. After all, cows have all those things, but the same people who complain about abortions don't usually have problems with eating meat.
But there's a related feature (well, more of a complex conglomeration of features) that isn't so obviously irrelevant. Is a fetus a person? That's a more reasonable question. But I still don't think it's relevant. Even if a fetus were undeniably a person, I'd still be in favor of the right to get an abortion. I'll illustrate with a hypothetical.
Suppose one winter's day, you accidentally leave your door unlocked. When you get home, you find that a homeless man has taken up residence. He doesn't pose any direct threat to you. He just takes up space, eats your food, and is generally inconvenient.
So, you decide to kick him out. "But", the homeless man protests, "It's freezing out there, and I have nowhere else to go! If you kick me out, I'll surely die!"
Is it morally prohibited to kick him out? Should you be required to provide him with food and shelter?
Now obviously, this hypothetical has a lot of differences from abortion. Here are the two I find most important.
One, homeless man is most definitely a person. A fetus may have a heartbeat, but this guy can talk. In the case of abortion, the status of the fetus is, at best, ambiguous.
Two, the homeless man is only taking shelter in your house, not your body. If you're allowed to decide who may or may not be in your property, surely you should be allowed to decide who may or may not be in your body.
And that's the important point of the abortion debate. It's not whether or not the fetus is a person. It's about whether women have the right to control their own bodies.