Could I go back in time- and kill Hitler, or Stalin or any evil person as a child- I would not kill them.
Should I even have a chance to go back in time and prevent my own mistakes and sins- I would not do so: I can live with my mistakes, because God hath given us confession.
Confession- in a way: turns back time- or rather: causes us to exist again.
This I would accept- to exist again- even as confession is as though it were: the equivalent of dying- as though I am a different person before and after- as though when I am in mortal sin- I only hold in proxy the place of Marc- Saint Named Philomena.
I would not turn back time to do evil that good may result- because I know that God only allows the minimum of sin and evil to exist. If we were to assassinate Hitler before his time- perhaps a greater evil would arise- now or in a thousand years.
Would I assassinate Hitler while the war was on, and I was there? Again- I doubt I would. One man makes not a war- nor can we predict the human ways. I would have fought against Hitler, however was most appropriate and moral- but I would not think assassination would be right. It is not how God chose to end the war- and there were many leaders of the National Socialist party (I hope I have rendered it right- I know National and Socialist were part of that heinous party's name).
Why we morally do not kill is as important as why we at times morally kill- or fight in frontiers- for good.
Violence when unneeded and misplaced- has been observed to increase injustice. America, once a great nation prior its genocide against the Japanese civilians, now routinely attacks nations, and has fronted Nazi ideals of killing children (I do not mean South African law's de jure definition) and the elderly- to the world, via its multiple organisations. America, also is the nation who most promotes methods of fighting disease such as HIV/AIDS which do not work- but which have accompanied a direct increase in the spread of the disease.
Evil is lack where our good should be. Good is fullness, in proportion with truth.
God did not kill Hitler as a child, nor did He who is wisest remove the tree of death from the Garden in Eden when the world- still was largely innocent.
It is wiser to obey truth- than beget falsehood. God says evil actions are lacking and should not be used to achieve good. He who controls the world- provides always better ways.