It’s probably not worth refighting this, but the promise of NATO and EU expansion avoided turning much of Eastern Europe into a potential Yugoslavia in the ’90s and did a lot to put the region on a democratic path. Practical, not utopian.
I don’t think Putin thinks in any sense that Ukraine is a military threat to Russia, but he does think that a reasonably democratic Ukraine poses a “threat of example” to his regime.
That’s the problem, not NATO. He also wants Ukraine’s resources, geography, and Slavic population; the last, of course, to deal with Russia’s tricky demographics.
The reasons may vary, but this is hardly a new thing. Yeltsin worried about it, and Solzhenitsyn talked about the need to maintain/rebuild the Slavic core of the former USSR (which included northern Kazakhstan, in Solzhenitsyn’s view) in the early ’90s, long before NATO expansion.