I think this is dangerously naïve.
There's a reason these countries spend what they do on their nuclear arsenals. The NATO members and the US in particular are well aware of when and why they would be used and that's largely what's dictating their response or lack thereof. Putin will know once NATO gets involved that he is completely outmatched conventionally - He would know that everything he's just staked his personal legacy on is doomed. How anyone could be confident that he'd back down in this scenario given how far he's already gone is beyond me. He's already put himself at huge personal risk with this invasion. This childish notion that bullies will always stand down when you step to them is just ludicrous - They have these nuclear weapons for a reason and there would be huge internal on pressure on Putin if his gambit has failed for all the world to see. In that scenario you're relying on a 70 year old man with little else to lose to do the graceful thing and walk away or blindly hope that someone launches a successful coup to prevent him escalating. That may happen, it might even be likely but I'm certainly not willing to risk civilisation for it.
The US, UK and NATO are fervently anti-Russia. They want nothing more than this hostile power taken out but they still don't budge on this for a reason. They know nuclear war isn't the sci-fantasy some seem to think - They know themselves how close things have come in the past even without the sort of existential threat that would be facing Putin. There's been pro's and cons to the existence of nuclear weapons but I think the cons far outweigh the pros. They make limited warfare an inevitability - You have the contradictory attitude to want to defeat and enemy but not too badly that they'll lash out. It's far too dangerous a game to play, especially with someone who's just put himself in an extremely fragile position.
This is a better response than your previous one to me, where you just called me insane, so thanks.
Nuclear weapons are a deterrent. Typically that has meant “a deterrent to protect one’s own sovereignty”, unfortunately the precedent that the Putin regime is setting is “the ability to go about your agenda unopposed”. This is problematic and escalators, and if he is allowed to get away with it (ie it’s shown that his plan works), then not only Russia, but other authoritarian states will follow suit.
Taiwan up next. The question is no longer “will the US defend Taiwan?”, the question is “will the US be prepared to blow up the world, for Taiwan”.
Putin is a rogue actor and essentially a terrorist. He is holding the world hostage, whilst he carries out his demands. The more you let him do it, the bolder he gets, and the bolder other states get. It’s a very slippery slope until you live in a world where all claimed territory belongs to one of a handful of nuclear powers.
We have to believe that there is still a middle ground, where conventional warfare does not lead to nukes being thrown around. If we defend Ukraine, but do not take a step onto Russian soil, there is no reason for escalation. Let Putin frame it in whatever way he wants to back at home with his propaganda channels. Let him claim victory in order to save face if he wants. Hell, let him keep Crimea. But show him that the west is prepared to defend itself.
Show him once, and show strength, and with any luck you never need to do so again - that is the best deterrent.
