I understand your longing for immediate action and I share the emotional need to cut off the snake's head sooner than later. Those who break the social contract of tolerance for each other should not be protected by it. Unfortunately it is a matter of fact that violence will always spiral out of control.
First you just want to get rid of the fascists. Assume you succeed and don't get reprimanded by law. Then you know how to get rid of someone and can act on it. What stops you to get to your rivals that want to strip you from your new found power? Chances are real you drift off into dictator mannerisms yourself.
The only way to not become what you try to eliminate is not to use excessive violence to begin with. Use the law. Use intimidating mass demonstrations. Use social pressure by making their views unspeakable again. Be better, stand for your values, organize with like minded folk and don't play into the stereotype of left groups always splittering into incapable small groups that cannot cooperate and coordinate
You assume that murdering people is somehow addictive. That is not true for sane people. See for example soldiers or self defense situations. The other commenter is right that sane people will stop being violent, once the threat is eliminated. Even some absolute psychos will only kill while it's acceptable and go back to suppress their desire for violence when it no longer is acceptable by their scociety.
At sone point violence may be the only way to defend freedom and democracy. However, I disagree with the other commenter that the time is now.
I should have worded it better - violence is the easy way. Easy is tempting. It's harder to debate with people. Inherently better, no doubt! It's a pattern in history that the number of people in power being corrupted by it is not low. Admittedly, not unfathomable high either, but it happens.
Last, sanity can slip in extreme situations and this, hopefully fictional, scenario is extreme in my book
The Nazis here meet in random places like mountain ranges at night time and the rare time they pop-up in protests it’s with police protection and unannounced beforehand.
Seems ridiculous, but true. By the way, by your own definition, you are cool with Nazis too, since you killed zero Nazis and let them even have nice gatherings in forests and mountains - perfect place to assault people if you ask me.