Subject: Re: Trump makes demands
I thought it had been pretty well established that prison neither reforms, nor deters. Always exceptions, of course. But in terms of the larger population, no. It just removes people from society for some amount of time.

I don't think that's correct. There's evidence that the certainty of being convicted is more important than the length of the sentence, which is used to argue against things like long mandatory minimums and life sentences without parole for less-than-capital crimes. Things like, a 90% chance of a 5 year sentence is a more effective deterrent than a 10% chance of a 20 year sentence. But prison itself does serve as a deterrent. So letting someone escape serving their sentence by getting deported immediately (if that were to be what happens) would reduce the deterrent effect.