Re: I've been wondering...
"Even though they just spent twenty minutes explaining that the girl's out-to-lunch and the world is in every kind of danger because of her?"
Yes, Wanda is a threat. The question is whether she's a threat that can only be neutralized by killing her, or whether there are other possible solutions, or whether there are no other solutions but killing her is less acceptable than letting her do her thing and suffering the potential consequences.
because if you don't then you might be killed.
And what part of that applies more to wartime than to superheroing? In fact, it applies less, because superheroes tend to be facing threats (threats of being killed, yes) from individuals or groups organized by a few key individuals. Killing those individuals would keep you from being killed much more effectively than killing enemy soldiers keeps you from being killed by the next lot of enemy soldiers. Wartime armies are national and big. If you are involved in a war you might be killed. That applies whether or not you are also killing people.
If someone attacks you in the street with a knife, would it be acceptable to kill them? If you don't, you might be killed, after all.
If you say yes, that's fine, and your moral code is internally consistent. If it's not, then I ask again, what makes wholescale international conflict different from individual interpersonal conflicts?
Killing in war has always been seen as more acceptable than killing outside of war. This is not because war is the only situation where killing would keep you alive. It's because war is the only situation where killing serves the interests of your society. Killing outside of war disrupts the peaceful running of society, so society wants people to see that as bad and not be prepared to do it. On the other hand, societies need people to be prepared to kill in a war, if they want to be able to raise an army to defend their interests. Soldiers have to be able to see the enemy as the bad guys, not start thinking of themselves as the bad guys for killing, or your army stops working as a cohesive body and starts questioning itself and ending up full of internal conflict. It's in the interests of a society to have killing in war seen as acceptable. But that requires you to accept 'in the interests of my society' as the same thing as 'right', and not question that. It's about more than the threat of being killed. It's about the nature of the source of the threat as well.