Physical violence is a necessity.

As you noted states can have tools against fascism and other takeovers themselves. Physical violence can be one of those tools first. Historically seen its the most successful tool. Nothing has made more fascists disappear than deadly force.

Simply taking away their platform and organisations is not enough. This isn't exclusive to fascism, but political movements in general. They will still remain a danger that way. They would still be a threat to real democracies, if we had any, by still being able to abuse and manipulate the system, swindling their way into power or undermining established constitutions, rights and laws. And in undemocratic systems they still can take over simply by corruption, propaganda or working their way up by more honest means.

It has been a while, but look at how in the 89-91 plenty of governments have been overthrown despite banned oppotisions.