We've said it before here, but I'll say it again: Having Ukraine fall to Russia will have terrible consequences on a geopolitical scale. If Russia establishes that nuclear powers can bully non-nuclear countries with impunity (sanctions are a joke), then you're going to get a lot more nuclear proliferation in the coming decades. Getting nukes is not that hard for a country, Pakistan developed their nuclear arsenal from scratch against the West's wishes and sabotage efforts.
If the reason why the west isn't providing more substantial aid is because they are afraid of nuclear war, then losing Ukraine all but guarantees its inevitability. As a result, I find it difficult to describe NATOs actions as rational. It's simply cowardice.
Though nuclear retaliation is a genuinely scary possibility (albeit less likely than the world thinks), the truth is that it's the lesser evil here. I don't want to live in a world where the Taliban has nukes.
This is a pretty silly take. First of all, you overstate the ease of "getting nukes" by a lot: Iran still doesn't have them (not for lack of trying), North Korea almost certainly managed to
lose theirs, despite both countries having the backing of
both of the most powerful anti-west nuclear-armed states. You mention Pakistan having them and the Taliban not having them, but Pakistan is, of course, the Taliban's largest backer. Pakistan certainly had a lot of help, both open and clandestine, just as India did. Indeed, since the Soviet Union intensively spied on the US nuclear program, there's not a single nuclear arsenal in the world that doesn't chain back to the Manhattan Project. And when it comes to getting help, at least since the fall of the USSR, countries have shown reticence to give away something like that. I can definitely tell you that pretty much all of Africa wants them, but they have yet to get any of their own and relations between African countries and Russia haven't gone that far yet either.
And even after "getting nukes", that isn't enough on its own: you must also have second-strike capability to reach the vaunted "bullying other states" status, which is harder.
Second, your argument can easily apply to every instance of a nuclear power bullying non-nuclear countries with impunity since, well, the first time; and nuclear proliferation hasn't happened recently. Why not the Russian-Georgian war, or the Second Chechen war, or the Gulf wars, or the Syrian war, or the US invasion of Afghanistan? Why not Israel and Palestine? Of course, non-nuclear states still bully each other at will based on who is stronger, and have since prehistory.
As to that, the reason the west isn't providing "more substantial aid" can hardly be said to be out of a fear of nuclear war in any long-range sense. There may be a specific fear for some of Ukraine specifically getting nuked and the west having to decide how to respond to that, but not of nuclear proliferation generally. Indeed, many people in positions of power have called for more escalation, not less. The limits on western aid to Ukraine seem to be mainly ability and will. While I'm sure they would have preferred better results, the leadership still view the current situation
in terms of the ground war as pretty close to the desired outcome.
Finally... the truth is that nuclear proliferation as a global force has pretty much jumped the shark. What is the use of a weapon you cannot use? Nuclear bombs are very expensive and do not actually kill people deader than any other means, of which we have plenty. Most countries have honestly realized this - they'd still
like nuclear bombs and prefer that their local enemies don't get them, but it's just not a really big thing. Actually, I believe Mohammed bin Salman said exactly that in an interview a couple months ago, with respect to Saudi Arabia.