You seem to think "killing mouthpieces" is going to be some magical event that makes hateful people reconsider (as opposed to spurring them to violence of their own).

Without recruiters and leaders, a movement is smaller, less coordinated, and less radicalised. This is doubly true of authoritatian movements built on lies.

Also, I'd like to add it's ridiculous hyperbole - 3.8 million people are estimated to have died in the 20 years of the Vietnam war. Just over 900k died to violence in all the post 9-11 wars in Iraq, Afghanistan, and Pakistan.

When talking about the threat of Western fascism, wouldn't it be more appropriate to look at western fascists? Hitler, Mussolini, Stalin... It's strange you'd point to such unrelated conflicts. Tens of millions dead.

You go ahead and be "guided by morality not legality" while you do try to convince others extrajudicial violence is alright.

If killing a mouthpiece of a genocidal movement prevents the deaths of tens of millions of people, it's morally correct. Similarly, gay marriage wasn't immoral until it was legal.

All because you believe killing people outside the law, and getting people killed in return, is productive if you're sure it's right.

Its right if it's productive. It's not productive because I'm sure it's right. You're tying yourself in knots here - it's very straightforward - minimise suffering and death.

You use the example of cops carrying guns, but they're not under license to kill everyone they disagree with nor is it considered moral (since you don't care about legality).

Cops carry guns because some violence is necessary, and desirable to stop more violence. You kill the school shooter to stop the kids getting murdered, you kill the Nazi leader to stop the minorities getting murdered. Attempting to spin this into a defence of killing anyone you disagree with demonstrates either willful dishonesty or a level of stupidity that would disqualify you from this conversation. Stop.

Violence should be a last resort

I've said as much.

used only within bounds that keep if from being a crime/war crime

Some killing is immoral and legal - e.g. the use of the death penalty, other killing is moral and illegal - e.g. killing Hitler to end World War II and the Holocaust. Why would you defer to legality in the context of fascists running the government, and being able to set the laws? Why was slavery immoral when it was legal? If your moral framework is based in legality (I don't think it is, I don't think you realise that), you're definitionally amoral - a fundamentally broken human being.

not exercised by everyone at will if they're pretty sure it's productive.

Are you going to wait for the fascist government to try the fascist leader, remove them from power, disassemble the means to commit their series of genocides, pack up and go home? This is a material defence of fascism.