yea they werent really a threat to russia imo
But they do exist and the documentaries about them from western media didn't portray them in a good light.
you can see why you wouldn't want them living next door, but then Russia is basically the reason they are like that anyway
Thing is, and something Putin touches on with the Nord Stream stuff, they claim they have evidence of the things (atrocities) they claim these Nazis have done, and I wouldn't be surprised if some of it is true, they've never even attempted to bring it up via the international organisations which exist to deal with this stuff, even if they believe they wouldn't get a fair hearing. And from everything I've seen while there has been some Nazi issues in relation to Ukraine it is very much a fringe thing while bad not even remotely justification to invade a whole country, especially not before exhausting the channels which exist for dealing with this stuff.
Azov were brought in under the regular military to try and manage some of this stuff.
EDIT: And as before these far right groups in Ukraine spawned out of Russian ultras so it would be a good idea for Putin to clear house domestically before making a big deal about Nazis in Ukraine.