Polygamy's legality today

This is my 1000th post on this blog, and King Solomon is said to have had a thousand wives, so it's only appropriate to mark the occasion with a post on polygamy.

Polygamy is now illegal in the U.S. thanks to a 1878 Supreme Court decision that declared it to be inconsistent with the principles of "civilized" nations.  Whether that opinion would survive in light of contemporary jurisprudence--especially the right to privacy--is a unresolved question.

A Christian law professor gamely gives it a try in Christianity Today and concludes--surprise!--that polygamy should remain illegal.  He recognizes that his arguments are kind of sketchy, though, so he builds up to the one that he thinks is irrefutable:

The strongest argument against polygamy is the argument from moral repugnance. Polygamy is inherently wrong—"just gross" as my law students say, "malum in se" as we law professors put it.

Y'know, if the "just gross" test is the standard for malum in se, shouldn't it also be a crime for middle-aged professors to hit on 20-something students?