I have no problem with the idea that we're going to kill in self-defense. Because, overall, we do. And we're gonna. Might as well recognize it. The principle of "don't kill in self-defense" is not transmissible. The best you can do is create a society where you're not having to choose to whether to kill others. Even 2A-believing cultures recognize this. "How about we don't brandish? Brandishing is just soooooo similar to an imminent threat that I just CAN'T". Even though, as someone in a non-2A culture, the difference between concealed-carry and a brandish is about, what?, seven seconds? In Canada, I see a concealed carry, I know I can start treating it like a threat immediately. (Amusingly, I'm not legally allowed to treat it like an imminent threat).
It's also interesting how many spiritual codes try to teach "don't kill in self-defense". They ask you to trust the universe to sort out the spiritual consequences. I've seen these people, my childhood church has supported more than one. Honestly, they're a very impressive and noble set of people. It's just not scalable. The religion that doesn't believe in self-defense can only be protected by religions that do, and that interpretation is selected for over time. (Alternatively, a successful transmission of universal peace ... good luck).
Killing in self-defense has some really interesting hypotheticals.
The other day, I was cornered in an alley by ten enemies that were intent on using their pipes and knives to kill me. Apparently, they'd mistaken me for this famous internet poster who'd ruined their friend's truck. Because their cognitive biases prevent me from talking them down, they feel like I've essentially volunteered for what comes next. In a way, we're all innocent. They've no intent to murder me, just murder.
Because I am a giant hypocrite, I have a revolver with me at all times. I brandish and they pause for a second. "Hey, he's got six bullets, and there are ten of us!" one shouts. I sigh. I can kill three hostiles with my bare hands, easypeasy. But not four. Four will kill me. I'm tough, but I'm not actually Tim.
The two moral questions are "may I (or even, should I) shoot him?" and "if they're not capable of being deterred, am I allowed to (or do I have an obligation to) kill six of them?"
It becomes a series of functions. By shooting the first person, I am trying to prevent one murder (me). But I am doing so by killing someone, and trying to create a deterrence effect. If it's guaranteed to work, nearly no one has an issue with it. Some do: see paragraph 2.
Some people think it's not only 'fine' but 'better' if I contribute to net seven deaths by taking as many down, even though none of my killing created my desired outcome (my continued existence). Some people will say that the first shot is questionable, and the second one is super questionable.