[Kevin]

From the perspective of someone who works in the area of family law, I hope bigamy/adultery are never declared illegal. While prosecutions never happen (and I don't really see the constitutional defect y'all are honing in on), the illegality does allow us to keep adultery from being claimed as grounds for divorce because as a practical matter, both of the alleged adulterers are going to invoke their 5th Amendment right to STFU when questioned about the alleged act or acts giving rise to the 'for cause' divorce.

In Oklahoma and probably most states, it doesn't make a lick of difference as to property division or anything else whether the divorce is granted for cause unless the proponent of that charge can further prove that there was an expenditure of marital resources in furtherance of the affair (usually tough to do).