You cannot do this with force.
Yeeaaah, all things else aside, bullshit. We already
have, once. Didn't make them completely gone, but it cut off the gas and the rest came later. It wasn't attempted conversion, but steady opposition up to and including violence and a persistent social effort to treat them as pariah that did it, after we, y'know, broke the back of their military forces and
nuked people. You won't find many people that are much more of a proponent of soft conversion as I am -- as I've said, Nazis are effectively the only goddamn thing in existence I think other methods starts off on the table and never leaves it -- but I'd be blind to not acknowledge that force is, in fact, a viable option when you're talking about stopping this particular ideology from doing harm. Necessary, beyond a point, because you have a fair bit of trouble discussing things when they're trying to kill you, your family, your countrymen, etc., etc.
We'd just like not to have to use it full throttle, again. Or even hint at having to, really.
You can't do it without force just as much as you can't with it alone, because to whatever degree violence fails to dissuade believers, anything less than absolute rejection does, as well, and harder. Giving up a whole slate of ways to stop this shit before it becomes (more of) a problem rather than after helps nothing. Particular when it necessarily goes hand in hand with a message that maybe these guys aren't
that bad, maybe there's room for something besides slamming the door in their face and applying boot if they try to kick it down. Which there isn't, when you're dealing with goddamn nazis. That this country softballed the bastards is the entire reason we're having this discussion at all.
You can work on conversion and your 20 Nazis (which, hell, if you've got a handful of years to work at it, might even do a decent job and more power to you for it) after the several hundred or several thousand aren't a concern, preferably because society has rejected them so hard they no longer have the means to be one. It's even a hell of a lot easier once congregation like that has been made effectively impossible, and any interconnection made more difficult. Nonexistent or ineffective are goals just about equally desirable when you're talking about a group specifically attempting to organize for murder.
Ideally it never reaches the point force is even warranted, but as MSH noted, when you've reached the point that there are Nazis walking down your street with flags and torches, yelling the ideology's screeds and beating protesters, as your country's primary leader softballs them for reasons who the ruddy hell knows, you're past the point you no longer have good reason to interact with the ideology's adherents without being armed or expecting violence.
I ain't gon' say much if you're trying to talk a nazi out of that filth when it's one on one or a small group, but when they're organizing and gathering in the dozens or hundreds or more it's reached the point they're a threat to anyone around them -- because being a threat to everyone around them is
literally their reason to exist -- and one very much sufficient to warrant force if less than that doesn't serve to disperse or contain. Which, y'know. Protesters beat with lit torches, murdered american, etc. If there was a way to talk that out no one managed it.