If it was their stance that a war crimes court is a bad thing, then it would be a fine, principled stand that I wouldn't have a problem with. But given that the US has never had a problem trying foreigners in war crimes courts (e.g. Nürnberg, or the whole Guantanamo/terrorist deal), they apparently don't think their constitution is good enough to apply it in a more wholesale fashion.

I remember Noam Chomsky saying something like "An argument whose validity depends on who is using it is merely an attempt at justification without any substance", and that seems a lot like what we're seeing here.