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
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