With the opinion of many people that executions are cruel. The US should be able to banish people and take away their citizenships. If they come back, then you shoot them. Murder, one strike and you are out. Rape, one strike and you are out. Child molester, one strike and you are out. All other major crimes, 3 strikes and you are out.
We have a lot of countries that accept a lot of aid from us, that we can conditionally release to them. Heck, some countries depending on your ancestry would probably accept them back also.
The taxpayer would not have to spend tens of thousands of dollars on these people, and instead that money could be diverted to something that will make this country better. And they get to spend their lives with their families someplace else.