@Lorenzo: As far as I'm concerned, the "psychological issue" (is Putin a madman?) isn't that relevant. Putin is a man in an extremely exposed position that implies an extreme lifestyle and behaviour, with a certain history, and surrounded by an environment that will tend to confirm his views. Perfectly normal people tend to perceive and believe what fits their prior convictions, and may behave erratically when they start to feel that things are going wrong. I don't think that any particular psychological diagnosis is required to explain Putin's actions, and many things that can happen (including nasty ones) are compatible with the absence of such a diagnosis.

I do think that discussing to what extent NATO's enlargement has contributed to the current situation makes some sense, although using terms such as "original sin" is rather inappropriate (and for sure doesn't look as if you "have many doubts and just want to discuss"). One problem with the idea that without NATO enlargement we wouldn't have this war is this: If you assume that the main reason for NATO enlargement was that NATO wanted to extend their powers, and as such it was something of an attack, and if you don't think that Americans or NATO people are particularly evil, you'd need to assume that enlargening the area of influence is a natural and common political motive and powers will generally tend to do that if they have the chance. But if this is so, you should well expect that also Russia, at a certain point after 1990, would have wanted and tried to do that, and the lack of extension of NATO would have given her a chance to get away with it on a larger scale. You'd basically need to assume that Putin is nicer and less offensive-minded than the Americans to think that the Russians wouldn't have done, at some point between 1990 and now, what the Americans have done, in your view, in the 1990s and early 2000s  Otherwise, NATO-membership of the Eastern European countries is perfectly justified (which is how I see things), given that they chose democratically to take part and nobody threatened them with war to get in.

Another thing that I wonder is what you think follows from your backward-looking analysis about who's at fault? What should be done now?

they haven't gone there (yet to this point)... and perhaps with good reason.  Just as we don't want to escalate this. So far Putin appears to not want to either as it seems Washington did get word to Moscow that doing that would be construed as a direct attack on America by Russia and an Article 5 trigger... and a big escalation even if it doesn't directly lead to troops or jets moving into Ukraine and direct military confrontation.

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In any case. The concern now is the well being of all the people caught up in this. The end would have to be a change in leadership in Russia. Putin would have to be replaced by leadership motivated by preserving th internal well being of the Russian people and not some old notion of preserving its past.