Okay, now. Who's first up against the wall?

Is there ever a time when it can be justified to put someone up against a wall and shoot them?
What if it was you?
I mean, it seems to me, the only reason these things happen is because of a difference of opinion.
It seems harsh to kill someone just because you are in a position of power and they disagree with you.
Let's take an extreme example.
Nazis!
They thought it was okay to gas lots of people who disagreed with them. They got away with it for a long time, mostly because the rest of the world didn't feel threatened enough to do anything about it.
The British farted about in Africa defending their colonies long before they took any action to stop Jews and Gypsies and intellectuals being shovelled into furnaces.
The Americans were worse. At one point they might have come in on either side.
But when it was all over, they set up a court and said this or that person should be put against a wall and shot. Well, I think they actually hanged them, but what difference? Maybe they should have crucified them.
Who gave them the right?
The British hunted Aboriginees to extinction in Tazmania. The Americans had a good go at doing the same thing. There are statues all over the bloody place honouring the pioneering achievements of men who instigated this genocide.
There was a point to this, but I can't remember what it was.
I'm going to bed.
I just hope someone doesn't drag me out of it in the middle of the night and shoot me because I prefer salty popcorn over sweet.