"Keep me from taking your purse" and "shoot you" we condemn B as a mugger.
"Leave me and meet someone new" and "shoot both of you" and we condemn B as a domestic abuser and potential murderer.
"Return a library book late" and "charge you $0.10 a day as a fine" and we condemn A lightly.
I would contend Russia's current actions fall squarely in the first two examples.
A: I want to take your purse.
B: If you take my purse, I will kill you.
If A continues to try and take the purse, A is obviously the agitator.
A: I want to leave you.
B: If you leave, I will kill you.
We agree B is a monster here, and this is a police matter, not global politics.
Maybe we can create a better example...
A: Hey B I want to nail your cousin.
B: I will not allow that to happen. Bro I will ruin your world. Literally, armageddon. Don't do it.
If A continues trying to nail the cousin, clearly the agitator.. no?
And I like how the only example you can think of where the word "agitator" flows well is when someone is trying to stop two consenting adults from having sex. Because clearly the person B on your last example is an asshole who is wrong, and you're using "agitator" to just mean "willing to ignore overt threats"
I think your own weak example highlights how you know you're wrong on this issue.
B isn't trying to take something from A. A is trying to woo (something near B) and B is promising consequences.
It no longer has anything to do about who is right, or what is right... that black and white right and wrong are no longer relevant.
If B is willing to back up the claims, A has to seriously consider their choices.
It's pretty close to the same in my example with the cousin... It doesn't matter if B is an asshole or is wrong, what does that have to do with anything?
The funny thing is, I don't think I'm even taking a position on the actual argument... I just think there's so much narrative control that many aren't even capable of considering alternative explanations.