IMHO, it's not promiscuity that is morally questionable, its promiscuity without the informed consent of all parties involved. Feynman had affairs with married

IMHO, it's not promiscuity that is morally questionable, its promiscuity without the informed consent of all parties involved. Feynman had affairs with married women (presumably without their husbands' knowledge or consent) and students, over whom he held power and whose consent (assuming they did consent) cannot have been free from coercion. (He also flat-out lied to women to get them to sleep with him, which is also not OK.) I think it's important to distinguish these situations because I think there are a lot of people going through a lot of emotional pain because they believe that any sex outside of a long-term monogamous relationship is morally questionable, and it's not. The challenge is that insuring that all parties have given informed consent is hard, but the emotional toll of throwing in the towel on this can be pretty high, so I think it can be an effort worth making. Certainly it's worthwhile telling people that it's OK to try.