I agree with your argument, but would like to add something about this part
Is it generally ethical to shoot people with guns to kill them? Generally not, I think we can all agree. What about shooting the SS soldier who has come to murder you and your loved ones? What about shooting the SS soldier who has come to your neighborhood not to murder you or your loved ones but one of your neighbors? In these cases most people who are not SS officers will agree these are acceptable times to kill. It’s still a terrible thing to kill someone regardless of the circumstances, but in these instances there weren’t other options. The reason there weren’t other options is that the Nazi party created an environment where certain groups of people had no option other than to escape by any means necessary.
Firing shots at the SS officier to protect someone is not the same action as executing someone (which is ehat the SS officer is planning in your example). Yes firing shots might kill them, but its not necessarily the goal of that action. I think there is a big difference between doing violence with the intent to kill and doing violence with the intent to stop, chase of or scare away.
That difference is why I agree with the "by any means necessary" sentiment of militant antifascism.