Perhaps it’s not so fallacious as you claim. Putin himself wrote a lengthy article (http://en.kremlin.ru/misc/66182) which was basically his version of Anschluß that Hitler used as reasoning for taking Austria in 1938. And Russian leaders have written a lot about how they would like to reverse the dismantling of USSR at least when it comes to territory – but since those nations are now sovereign that would amount to annexing those countries.

That article doesn't say what you seem to be claiming here.

I was talking about the precedent of using nuclear weapons to back offensive actions. USA did something like that during Korea in the 50s, but to my knowledge not since. Well ok, there was Trump, but who knows how serious that was.

And as you yourself admit the precedent is set by US which is the only country to actually commit such an atrocity. However, the bigger point here whether might makes right, and that's the rule that the west has consistently followed.

Didn’t Ukraine remain neutral about NATO until Russia took Crimea? Only after that they reconsidered that position.

No, Ukraine had a violent coup in 2014 where the legitimate government was overthrown and right wing nationalists took power. Russia annexed Crimea in response to that because the regime that took power started doing these sorts of things to the Russian speaking population:

• https://www.hrw.org/news/2014/10/20/ukraine-widespread-use-cluster-munitions
• https://twitter.com/paulius60/status/1611148483859255296