Putin might nuke Warsaw an hour after the no-fly zone is imposed. He's that crazy.
He has a difficult time winning the war already, he’d never be able to win if he pulls in more countries.
As always, apply the Falsifiability principle: https://en.wikipedia.org/wiki/Falsifiability
> the Kremlin said that Mr. Putin had told his French counterparty
> that his main goal was “the demilitarization and neutral status of Ukraine.”
> Those goals, the Kremlin said, “will be achieved no matter what.”
The only English source I could find quickly was this:
https://www.nytimes.com/2022/03/03/world/europe/putin-macron...
Russia is desperate to deter EU/USA from involving itself more in the war, and the only way it can do that is by treating to escalate to nuclear war.
But that threat is only effective if people actually think that you will do it, so they must play this so that they seem crazy enough to start a nuclear war.
It's a bit like someone blackmailing you for money for something illegal you did together, only way to get you to pay is to show that they are really willing to expose your secrets, even if they might be exposed also. And once you believe them and start paying they will continue to demand money from you.
Edit: by your terminology I would consider Ukrainians to be crazy. This a good thing and the reason why I’m rooting for them. They’re the underdog. The rational thing for them to do was to capitulate as soon as the invasions started. It takes a “crazy” level of conviction to the do the irrational thing here.
If you think they might not, because ethics and morals, then the deterrent's value is discounted by your percentage of doubt.