Strick, I'll take a pass on the hat rack discussion; greater minds than mine can weigh in on that one.

As for the other two, I was referring to sexual behavior when I used the phrase "consenting adults". Whether or not we should allow incestuous and/or polygamous marriages is a different (albeit related) question. I will confess that they make me uncomfortable, but I agree with you that my discomfort shouldn't be the determining factor, any more than someone else's discomfort with homosexual marriage should be the determining factor in addressing that question.

I would want to examine the legal aspects of your question before giving a definitive answer. Government's role in this question should be limited to the legal/contractual aspects, and any prohibition of these sorts of marriages should be based on identified legal wrongs that would result from allowing them. For example, while I am not an expert in contract law, I do know that a contract between two parties brings different considerations to bear than a contract involving multiple parties, which may have some bearing on the polygamy question (particularly when potential divorce, child support, and similar issues are considered). There may be some comparable considerations in weighing the question of incestuous marriages, along with the medical concerns others have already raised.

What I would NOT do is seek to prohibit these sorts of marriages based on religious, cultural or personal objections. These have no place in a country whose Constitution explicitly prohibits the passage of laws respecting one religion or another, and they also have no place in a country that proudly proclaims its multicultural character and its respect for individual rights.