Eugene Volokh has a lengthy post questioning the wisdom of an Oklahoma state legislator’s proposal to define any sexual activity between a student under 21 and a university employee as “rape”.
I tend to agree with Eugene’s position—the position, incidentally, staked out in the most recent addendum to the Millsaps faculty handbook (I think; I’ll look it up when I’m at work tomorrow)—that relationships betwen faculty members and students they are currently instructing are inappropriate, for a variety of reasons that he details in his post. I generally also think that faculty members are just asking for trouble if they get involved with undergraduates—whether or not they are responsible for assessing their work—but I can’t see any good reason to make consensual sexual conduct illegal as long as both parties are over 18.