There’s the possibility that gay marriage might be legal in Illinois. This means we are subject to arguments such as the ones discussed in this article. Here’s a snippet of the argument:
“Marriage comes to us from nature,” Chicago’s Cardinal Francis George said in a recent interview. “That’s based on the complementarity of the two sexes in such a way that the love of a man and a woman joined in a marital union is open to life, and that’s how families are created and society goes along. … It’s not in our doctrine. It’s not a matter of faith. It’s a matter of reason and understanding the way nature operates.”
Actually, it’s not “a matter of reason” but rather an empirical claim, a false one it turns out, about how marriage operates in nature. Animals, it so turns out, don’t ever get married.  Some are not monogamous in their unions, some even gay.
Here’s a screenshot to the same article which expresses the Cardinal’s attitude toward having a serious discussion:
Anyway, let’s hope this is over soon. The Illinois version has not made these natural law arguments any more cogent.