Speaking as someone from the US, a signatory to the Budapest Morandum, guaranteeing the sanctity of Ukraine's borders in return for giving up nuclear weapons - and that as a signatory failed to support Ukraine with a solid military response (starting with a no-fly zone) when that memorandum was violated in 2014 and more recently in 2022 we have no right at all to tell Ukraine whether they should re-arm or not.
The real question is, once they rearm, then what happens? Do the Russian gangsters attack preemptively, which almost certainly will result in a (probably non-nuclear) response from the West and another (probably nuclear) one from Ukraine. Do they do nothing, keep on killing Ukrainian civilians with glide bombs, keep sending meat-wave attacks? Do they stay where they are, turning front lines into defacto borders?
I've no answers, but I think the last possibility is the most probable - but I don't claim to understand Russians, nevermind Russian gangsters.
Then, once Ukraine has nuclear weapons, what happens to relations with the West?
Trump's a moron, but what do his security people do when it's a choice between 'support Ukraine' and 'nuclear exchange'. Based on his announced cabinet picks I an *not* expecting a rational response. Complicating that, RT has been publishing nude pictures of his wife. Given that it's RT, I'd expect it's gotten the go-ahead from Putin. Not sure how they expect that to help them - but it can certainly backfire.
Then there are the European centers of power. Once Ukraine becomes probably-nuclear, does that make admittance to NATO more or less likely. I'd guess 'more', as that would seem to make a nuclear exchange less likely - but if you read the NATO charter, there's a ban on admitting any country that has an 'ongoing border dispute'.
Just thinking it through - and I have mostly questions...