I agree in general but slight nitpick:

When somebody declares intent to harm you, proportional violence becomes justified as self defence.

If you say you want to hit me on my pinky finger, I'm not justified in killing you. If you declare to kill or eradicate me, as the extreme right does to certain marginalised groups, a lot of different levels of violence are justified, including killing for the really severe cases.

That depends.is this hypothetical man to my right or to my left?

So, fun and slightly unrelated story:

In the late 80s, when I was a teen, we were driving through the Arizona desert to Mexico and there was this big stretch where there was just nothing. No radio, no rest stops, literally nothing. And I had to pee really bad.

So we pulled over for me to do my business. It was an open desert with nothing to hide behind, so I went a bit from the road and found the biggest bush I could. It was dead and not full enough for much privacy, but far enough that I thought it gave enough cover. So I squatted and pulled down my shorts, and heard a really loud rattle. I didn’t even think. Just scrambled back towards the car, butt naked to the sky, scraping my knees in the dirt. Not even sure when or how I pulled up my shorts.

I’d nearly pissed on a rattlesnake. The adults reassured me that they rattle instead of bite, so I wasn’t in real danger. They thought it was hilarious. I did not.

Sometimes you don’t think, you just do what you can do.

If you see a snake coiling up and preparing to strike, do you wait until it bites you to stop it?

Generally speaking, snakes only attack when they feel threatened.

But humans attack purely for the joy of killing.

If I see a snake coiled up to attack, I back away and we both live another day. I don't reach in to stab it, get bit in response, and die from the poison a few hours later.