Everyone who is pro-choice will have a moment that challenges that belief. No matter how hard-line, pro-abortion, pro-contraception, there will be a moment when the temptation is to limit choice. It could be multiple abortions, or late-term abortions, or parental notification, or drug use during pregnancy; an issue that forces people to confront their own emotional reactions and assumptions about choice.
Failure to fully confront their own reactions is what leads some people to become pro-choice-but. "I'm pro-choice, but I don't think that women should get lots of abortions." "I'm pro-choice, but I don't think that women should have abortions for just any reason." "I'm pro-choice, but I believe that women should get their parents/partners permission." "I'm pro-choice, but I think that women should be prosecuted for drinking/smoking/using drugs during pregnancy."
I found mine.
I'm not at all comfortable with fertility treatments being used to allow women over 65 to become pregnant. I don't think it's a good decision. I think it's a waste of money. I think that it's not fair. BUT. I refuse to become "pro-choice-but". I won't do it.
Becoming pregnant, even at 67, is choice. And I do not, and refuse to allow myself, to support any kind of restriction on who can become pregnant, and by what means. I may be uncomfortable with it, but I don't think I'll ever be uncomfortable enough with anything to believe that my discomfort is worth someone else's choice.