I understand the argument that maybe the United States didn't have the right to kill Saddam. But let's not forget that he and his sons tortured generations of Iraqis. If Saddam were still alive, I'm sure he or his family would have made a gran for power somehow and the Iraqi people would suffer again.
Saddam Hussein was a dictator who used his power against his opponents in Iraq. He was a terrorist and deserved to die. The United States could have killed him when the invasion took place but instead their option was to hand to give him to the authorities to follow a trial and his final death.
The United States had the right to want Saddam Hussein dead. However, America did not actually kill the former Iraqi dictator. Instead, Hussein was put on trial in Iraq, convicted and sentenced to death by hanging. It was the Iraqi government which ended up killing Saddam Hussein, not the United States.
Personally, I think in that part of the world, you need dictators like Saddam. He was the only person that could deal with the terrorists there. We got involved in Iraq for very questionable reason, removed him and now ISIS exist where it wouldn't if we never invaded. Bad person, but removing him was proof that our style of government in that part of the world is a very bad idea.
He was a hard, callous man and his boys were twisted, but he at least kept a lid on a region of the world still living as they had for a thousand years. It is hard to tell what he would have done as he reached the end of his life and what he would have decided to leave behind him. The US helped put him in power because they believed some one like him was the only option to control the region...
For a government killing person one might see it to be alright. But as like death penalty, none should be allowed to decide for someone else's life. Not even as a warning, not eve as "an example what happens if you don't obey". That is why I see all killing as a bad and a wrong thing to do.
The USA, did not kill Saddam. The new government tried, convicted and executed him. Because US did not offer Saddam asylum, nor the option of seeking refuge in a country like France—for example—you could make the case that US had a part in it, because US turned him over.
Whenever a new government is installed, following a war, or during a war, there is a purge by blood, banishment, asylum or execution. Prison is also available if it is deemed that the persons are not a threat to the government coming into power.
The change of power is really little different than the way Saddam came into power; a bit more democratic, perhaps, but not much different.