Yeah the primarchs do it, and it’s kinda weird. But they are inhuman monsters that have to serve as generals and politicians, so I forgive them.
When space Marines do it the it’s kinda like how priests refer to each other as brother, but also battle brother is a rank.
I think it is also there to make things seem more theatric/dramatic. Like just how many books start with a dramatis personae? We’re not reading about people, we’re reading about characters in a space opera. No matter how you look at it, it’s still pretty silly.
Ah, because whoever they kill is definitely an enemy. If they were already infallible why do they need AI?