Well, what’s wrong with it? Doesn’t the professor who faces criminal charges for having sex with his adult doctor have constitutional rights? Isn’t it true (see LAWRENCE v. TEXAS) that two autonomous persons can express themselves any way they please as long as what they do is safe, consensual and between or among adults. We used to say incest might produce little monsters, so to speak. That’s not so clear, it turns out. And in any case, the objection doesn’t apply to safe incest. Incest, we learn from Aristophanes onward, is really bad for the proper sort of loving relationships that constitute a family. But the Court seems to say that protecting the family can’t trump autonomy, because marriage is nothing but a contractual connection between two autonmous individuals. People are free to believe that what the professor and his daughter did was disgusting and not engage in such behavior themselves. But we really find it just about impossible, as Matt Franck observes, to explain why such behavior should be illegal.
If a man can have sex with daughter, does have the right to be able to marry her?