There are really only three answers to this question. All are deeply problematic:
1) No time. The justification is usually that women weren't punished pre-Roe, and therefore don't need to be punished now (that's the implication in JivinJ's post, linked above). The trouble here is that now you've just given the fetus an infinitely smaller legal value than any other life, and than any other crime against property, privacy, or bodily integrity. And it implies that abortion really isn't murder, and that the fetus really isn't as human as other humans. In fact, it creates a legal second-class category for fetuses, which is exactly what anti-choicers want to avoid.
2) Some time, but with a lot of lenience because you have to be crazy/emotional/hysterical to have an abortion. This answer is the worst of the three, because so many women are prepared to have abortions before they actually end up in a position where they have to. I did some hypothetical math on the comment thread:
let’s imagine that even as few as 20% of women will identify as prepared to consider an abortion if they were to have an unwanted pregnancy. That means that of the roughly 1,200,000 legal abortions in the U.S. every year, an extremely conservative figure of 240,000 were already prepared to have an abortion before they apparently came down with a fit of hysterics due to becoming pregnant. That’s 240,000 clear premeditated murders.
So number two basically equates to:
3) Ship 'em off to prison. This one is the most logically consistent, but not only is deeply alienating to all but the nuttiest of the wingnuts, but also is fairly socially unsustainable. Here's some more hypothetical math:
About 1.4% of murders currently result in the death penalty: that’s maybe 3,300 more executions every year. Not to mention the other 230,000 life prisoners we would need to incarcerate. So even if “you’d have to be crazy to have an abortion” were to fly 80% of the time (and I’m not even talking about what that argument would mean in terms of infantilizing women), that could still mean an incredible glut of incarcerations and executions. Even if we were to imagine that abortions were to drop to pre-Roe levels (around 580,000/year, according to the CDC), that’s a shitload of women getting thrown into prison and jabbed with a lethal injection.
I'm not going to go on about the prison crowding problems this country has, but suffice it to say, we couldn't imprison women who got abortions if we wanted to.
There were a few other interesting thought experiments that came up in commenting, and near the end of Jill's post. The first was Jill's:
There’s a fire in a fertility clinic. Inside the clinic there’s a three-year-old boy who you’ve never met and have absolutely no connection to. There are also 100 embryos in a box. You only have time to run into the clinic one time. You cannot carry the boy and the box at the same time. What do you do? Do you save 100, or do you save one?
The best anti-choice answer to this one was that life is infinitely valuable, and it's impossible to decide. I've heard this argument before, and it's equally uncompelling every time. A good way around it is to think about the state of the world in either situation. If we can save one person or three people, the world is two people better off if we do the latter. And this isn't a hypothetical problem. Medical triage makes these choices all the time, with regrettable but necessary results.
Someone, I forget who, posed this situation: a woman will die of cancer unless she gets chemotherapy. That chemotherapy will cause her pregnancy to spontaneously abort. She will live long enough without chemo to give birth to a healthy baby, but by that time it will be too late to save her. Should she have chemo? I'd add: what if the chemo has only a 50% success rate? 10%? At what percentage do we flip a coin? Because at that point, I think, we have the relative value of a healthy, wanted fetus to its mother.
Why are these questions important? They establish the relative values of social goods, and that's what lawmaking is all about. Do whatever you want with your personal ethics, but if you can't answer these questions, and well, I don't want you making my laws.