Well, but the examples I provided were not only found constitutional, but at the time they were found to be constitutional, they were also democratically popular. To answer your question “What’s left?”, I don’t know. It made me think of this speech by Seward, though, for some reason:
http://www.furman.edu/~benson/docs/seward.htm
At any rate, ultimately, extradition is a Spanish (or French, or German) decision to make. They captured and are holding the prisoners, and so those states have a responsibility to their laws and their values that these prisoners be treated according to the values they hold.