There appear to be plenty of people with that position (at least where I am) even looking at revealed preferences. (Specifically: the number of sexually active girls I know in my home town who have had a child in their teens isn't much smaller than a Fermi estimate of the number of them who would have gotten pregnant at some point (ETA: based on what I know about the failure rates of contraception), so there's a sizeable fraction of people who decide not to abort their own children. OTOH I can't see many people doing anything to try to make abortion illegal. Now, it could be that those girls for some reason are less likely to abort than the general population, but “high-school students, often politically left-wing” is about the last demographic for which I'd expect that to be the case.)
EDIT: According to http://en.wikipedia.org/wiki/Abortion_in_Italy, “[a] proposal to repeal the law [allowing abortion] was considered in a 1981 national referendum, but was rejected by nearly 68% of voters” (and given the fact that the quorum for referendums to be valid in Italy is the majority of people eligible to vote, lots of the people who want to keep the status quo will usually just stay home and not vote), but “[i]n 1993, the abortion ratio in Italy was 9.8 per 1,000 live births”. Now stuff might have changed in those 12 years, but still... (Nice that wild-ass estimates I got from just looking around aren't way far off.)
EDIT: I know there likely are lots of clandestine abortions going on in certain parts of Italy, but even if the statistic of 9.8/1,000 was off by a factor of --say-- 3, my point would still hold.)
Forgive me if I have misunderstood you, but you appear to be saying:
I do not see how (4) follows from (1), (2) and (3). Firstly, getting pregnant is a benefit as well as a cost - being pro-choice doesn't mean you will ...
Or is the convention against discussing politics here silly?
I propose a test. I'm going to try to lay down some rules on voting on comments for the test here (not that I can force anybody to abide by them):
1.) Top-level comments should introduce arguments (or ridicule me and/or this test); responses should be responses to those arguments.
2.) Upvote and downvote based on whether or not you find an argument convincing in the context in which it was raised. This means if it's a good argument against the argument it is responding to, not whether or not there's a good/obvious counterargument to it; if you have a good counterargument, raise it. If it's a convincing argument, and the counterargument is also convincing, upvote both. If both arguments are unconvincing, downvote both.
3.) Try not to downvote particular comments excessively, if they're legitimate lines of argument. A faulty line of argument provides opportunity for rebuttal, and so for our test has value even then; that is, I want some faulty lines of argument here. If you disagree, please downvote me, instead of the faulty comments, because this post is what you want less of, not those comments. This necessarily implies, for balance, that we not excessively upvote comments. I'd suggest fairly arbitrary limits of 3/-3?
Edit: 4.) A single argument per comment would be ideal; as MixedNuts points out here, it's otherwise hard to distinguish between one good and one bad argument, which makes the upvoting/downvoting difficult to evaluate. (My apologies about missing this, folks.)
I'm going to try really hard not to get personally involved, except to lay down a leading comment posing an argument against abortion, a position I don't hold, for the record. The core of the argument isn't disingenuous, and I hold that this argument is true, it just doesn't lead to my opposing abortion. I do not hold the moral axiom by which I extend the basic argument to argue against abortion, however; I'm playing the devil's advocate to try to help me from getting sucked into the argument while providing an initial point of discussion.
Which leads me to the next point: If you see a hole in an argument, even if it's an argument for a perspective you agree with, poke through it. The goal is to see whether we can have a constructive political argument here.
The fact that this is a test, and known to be a test, means this isn't a blind study. Uh, try to act as if you're not being tested?
After it's gone on a little while, if this post hasn't been hopelessly downvoted and ridiculed (and thus the premise and test discarded as undesirable to begin with), we can put up a poll to see whether people found the political debates helpful, not helpful, and so on.