I would always say, if we justify some killings, there is always a chance people will abuse this “loophole” for crime we created.

Oh you mean how UHC uses that loophole to kill people with social murder, and our moral system doesn't consider it a crime because they didn't directly stab someone to death, but instead purposefully denied them care that they had paid for by paying for insurance, leaving them to die.

So saying all killings are illegal is kind of the best application of our morals we have.

Except, we clearly don't say all killings are illegal, as evidenced by what I just discussed. We have clearly made the choice that social murder though things like denying healthcare or denying housing and pushing people into the frozen deadly streets of winter are totes okay. That's literally what's at issue here, is that a whole swath of killings are allowed, and not just allowed, but are allowed to be profited from, and handsomely. Which is far darker and worse, imho.

Genuinely, it's easy to say that we have banned all killings, but we clearly haven't. Cops even have qualified immunity to murder with impunity. We have the largest military in the world, and we've been known as the violent "World Police" that will bomb your country to the fucking stone age. Those deaths and that violence is normalized. That's why they say "the state has a monopoly on violence."