If asked about whether abortion should be illegal in the case of rape or incest, the proper answer is along the following lines:
"If by asking that question you are implicitly agreeing that abortion should be illegal in the 99% of cases having nothing to do with rape or incest, then this is great news. You and I have plenty of common ground to cooperate in ending the scourge that is abortion. In that case I would ask you what is your principle for saying that abortion should be illegal in the 99% of cases and why doesn't this principle apply to the innocent children conceived by rape or incest? In any event, surely you agree that it would be barbaric to sacrifice the innocent children in the 99% of cases we do agree on simply because we cannot in the meantime agree on what to do for the cases of rape or incest?"
"Now if you are asking this question but see nothing wrong with abortion in the 99% of cases having nothing to do with rape or incest, then your question is, logically speaking, wholly irrelevant. Depending on your motives for asking, the question also may well be cynical, manipulative, and, quite frankly, insultingly demagogic, and I can give no answer other than to note these facts."