A few stable nations with nukes has created the longest stretch of world peace in recorded history
There are multiple aspects to unpack.
While that peace is true, it is not all encompassing. Been plenty of war and violence since WW2.
Yes, it is not to scale and has been somewhat contained thus far. The fleeting hope is it remains contained.
Invading Ukraine for Genocidal conquest and sending 10s of millions of refugees into NATO is going to put that to the test. Do we sit back and watch 44 million neighbors get slaughtered? Okay, so we (barely) arm them and watch them fight and die to fend of ethnic cleansing on our door step. A rather chicken !@#$ way of saying we're with you
But that peace is temporary. You said stable nations, but no nation will remain stable. You can claim victory of peace only for a duration, and while delusions may settle in while the peace holds, never forget what human nature actually is. Even if it takes a few hundred years, we are destined to break our bonds. Unstable nations will neither give up their nukes, nor handle them responsibly. Every nation is merely a matter of time before it reaches that stage. And irresponsible handling of nukes will see them used, one way or another.
Russia is already testing instability via threats of nuclear blackmail. Let them genocide 44 million people (to start) or else. That's a new level of nuclear depravity. It will get worse.
Beyond that, Russia has proven that anyone not holding nukes is fair game. This is a massive impetus for either joining NATO or nuclear proliferation. More nuclear weapons will be made to try and fend off the existing nuclear powers. Agreements clearly are not real, and this invasion even asks the question... would NATO defend itself and risk MAD? We clearly will not risk it for 44 million neighbors, and the only benefit Poland enjoys is... a piece of paper. Ukraine had one too. Why "end the world" and "commit suicide" over someone else?
Our policy is deeply flawed and contradictory. The only thing we can be certain of is this. Our world is becoming more dangerous, more nuclear, not less. To that end, I will ever condemn nuclear proliferation. While it has had some benefits, there will be a terrible price yet to be paid. And choosing which nations to save from genocide is not helping.
It must be all nations. Or they will feel the need to go nuclear.