I personally think that abortion is immoral. But I don't think that everything that is immoral should be illegal. Marital infidelity is also immoral, but I feel strongly that it shouldn't be illegal. In the case of abortion, I don't know how I feel (nor what I should think) about the legal question.
So my general question is this: is the inference from the immorality of some act X to the claim that X ought to be illegal ever justified? If not, why not?