Why do polls show more Americans calling themselves "pro-life" without a corresponding increase in the belief that abortion is morally wrong?

Gallup's hypothesis is that "increased political polarization... particularly since Barack Obama took office" has made more people want to adopt the label "pro-life."

Now, I think that "pro-life" means an opposition to the legal right to access to abortion, and that one's position on the legal question can and should be distinguished from one's conclusion about morality. We can support individual liberty to do a lot of things that we think are morally wrong — lying to friends, cheating on your spouse, destroying useful possessions instead of giving them to charity, etc. etc. But that insight isn't helpful in explaining the discrepancy Gallup identifies. Although I can see why more people could come to believe that abortion is morally wrong without wanting to deprive women of control of their own bodies, the trend in the polls goes in the opposite direction. The moral opinion is stable, even as more people are saying they are pro-life.

It would be good if the poll had a question asking people to pick one of these 4 categories:

1. abortion is morally wrong and should be banned or severely restricted
2. abortion is not morally wrong and should not be banned or severely restricted
3. abortion is morally wrong but it should be not be banned or severely restricted
4. abortion is not morally wrong but it should be banned or severely restricted

I'm saying I understand — and I personally agree with — #3. And I don't think the poll shows an increase in #3. I think #4 is the strangest idea, and the Gallup results look as though it is the increasing category. Since that is unlikely, I'm inclined to accept Gallup's hypothesis that the label "pro-life" has become more popular — at least when answering questions asked by pollsters. Are there also more out-and-proud pro-lifers these days?