Main issue I have with life imprisonment right now is that criminals have access to many leisure activities, and even though they are separated from society, they are treated extremely well and many of them do have private interaction with other people. For all the complaints of Amnesty International (other idiots, etc.), American prisoners have some of the best conditions in the world (you should see what the French prisoners get, for example; of course they don't stay in prison very long).
I would be fine with a system with no death penalty that made the murderers work in manual labor 15-16 hours a day with no leisure activities, on basic food and water and base sleeping conditions, with no interpersonal activity. (and probably a little torture too
).
But that's not going to happen because of one major reason: The USSC would probably rule it unconstitutional due to violation of the 8th Amendment "cruel and unusual punishment" provision.
So, the alternative is clearly better, first because talk and references to the death penalty in the Constitution are numerous (and are therefore unlikely to be viewed as immaterial), unless we get more Brennans or Marshalls on the court (egads!), and because death is never a nice thing for a prisoner. I doubt it's a way out except for only the weirdest criminal minds and most of those people would have committed suicide at one point or another, anyway, so its no loss.
