I would hope that describes virtually every post war western government.
And many of them have implemented various levels of 'authoritarian' systems to prevent the (re)rise of Nazis. Ranging from the banning of books in Germany to more mundane things like the British police spending a lot of time and money infiltrating neo-nazi groups and banning them. In the latter case exactly the kind of thing you are worried about happened - the powers granted to the police were also used to target other non-nazi groups like environmental protestors. Despite being very critical of police tactics in the latter cases, I still have no problem with the police targeting Nazis.
Anyway, western governments don't need to raise the spectre of Nazis to gain support for increased police and surveillance powers. They have plenty of more recent things to talk about (from Irish terrorists to ETA to Islamic terrorists). This comment thread is evidence enough for that - there wouldn't have been nearly the same emotional reaction to somebody talking about bombing ISIS.
So what you are saying is, that all the police have to do is label someone a Nazi, and you'll give them a free pass for whatever it is that they do?
I do think the police should act to try and prevent violent groups from committing violence. Your position seems to be that the state should accept violence as long as the people committing it claim to be political? If anything organised political violence is the type of violence that it's the most important to prevent because it has by far the largest potential for harm.
I can talk about specific things the UK police have done when targeting 'extremist' groups and how I disprove of them if you want (undercover police assuming fake identities to the extent of having children with women in the targeted groups being one). But disapproving of specific things isn't the same as saying the police shouldn't be investigating and infiltrating organisations advocating violent ideologies.
It is dangerous to believe "oh, I don't care what an oppressive government does in order to stop Nazis" because a whole lot of people are being called Nazis these days.
The same exact thing happened during the red scare. It was not JUST the revolutionary communists who were literally trying to overthrow the government that got oppressed. A whole lot of other people who definitely didn't deserve it, got oppressed to.
Human rights exist for everyone for a reason.
What people tend to forget is that all totalitarian systems that came to power, have their origins form reactive movements acting to ineffectiveness or oppressiveness of existing systems. NSDAP was formed in response to worsening national situation. Reds and Whites were formed in response to worsening national situation. Italian fascism was response to political turmoil in post-war Italy. Quite a few European countries romanced with authoritarian rule (or went borderline fascist) in inter-war period.
Let me turn this question around: what if anti-nazi party came into power, and then to assure that no nazi party would ever come into power, it would implement its own authoritarian system? After all a lot of those governments enjoyed popular support during their rise to power, with people willing to give up their freedoms for sake of perceived security.
Back in McCarthyism it was better "dead than red". What if "its good to throw the nazi off the copter" is just a sign of our societies marching to new era of scare?