Seems to me that the position that the death penalty is barbaric is a bit passe and naive. The idea of a final punishment for certain proscribed actions is not cruel in and of itself. I would agree that there are more humane ways of executing someone than hanging them, but don't buy into the argument that the dp is itself somehow evil. If you wish, on the other hand, to address how it is applied (circumstances leading to), then that is a different story altogether and fit for another thread.
As to Saddam, it would be foolish to think that keeping him alive would be any safer than swiftly executing him. From prison he could still try to exert influence or possibly even be broken out of prison. Also, putting SH in charge of Iraq to clean it up would be insane. We'd most likely have to go back in again in 10-12 years (or even sooner). However, the left would certainly shut up about all the torture he'd commit after we left b/c there'd be no political mileage in it for them.