The Rockerfly said:
Would you let Hitler live? Exactly
It is not as clear cut as that, personally, no, but then again I would, if given the chance blink a lot of people out of existence.
First of all there is the religious argument, if you do believe in the 10 commandments, then no matter how you look at it, Killing is wrong, and if you are of that conviction then the question becomes, your soul or Hitlers death.
Secondly, there is the butterfly effect.
Sure killing Hiltler during his failed art student phase seems like a gimmie, but then again without the Nazis how do you know that Stalin would not have sent a red tide of equally horrednous proportions across Europe/The world.
No Hitler would mean no influx of German scientists to the US, No space program, that alone would probably set the USA back 40 years.
Back on Topic
If you can be 100% sure of guilt, then I would vote to execute all rapists, pedophiles and murderers.
I think manslaughter is a different thing.
But again I want to specify 100% sure has to be irrevocable evidence, not a "crazy man" confession. I think you need to be completely sure.