You really ought read up on the facts before you spout nonsense.
Do you really not know that Arbery was the aggressor here? That Arbery took a swing at the son? That Arbery lunged at the son and grabbed the shotgun?
These are facts, son. Not opinions.
Why did he do that? You cannot start the story in the middle. Did they guy simply walk up to him with a gun, without any reason.
I asked you before if you thought this was a morally justified killing.
If you think it is, it answers a lot of questions.