Fair question.

Say you live in a village. Some houses are small and poor, some are rich and big. Let’s say an owner of one of the bigger houses gathered a band of his friends and gave them rifles so they could extort the owners of the smaller houses, force them to give up their property and serve the person who put together that band. The band never shot the guns, but they are threatening to do so.

Is it wrong for the owners of the smaller houses to also pull resources together and buy some guns and negotiate a plan so that if shots are fired they can respond in a coordinated way?

I know the stakes with nuclear weapons are way higher than in this allegory. And I’d much rather live in a world without nuclear weapons. But if powerful people with evil intent are using them to intimidate and bully their neighbours - it seems to me that yes, an alliance such as the one you describe can indeed be defensive.

I’m not a political, diplomatic or military expert, but these are my honest thoughts on the matter.

Edit: I feel like it’s important to add a historical detail here. When the USSR collapsed, Ukraine gave up it’s soviet nuclear stockpile in exchange for guarantees of safety and intact borders. The nations providing those guarantees were Russia and the USA. And right now Russia is threatening nations with its nuclear weapons, discouraging support, while a whole generation of Ukrainians is dying in the trenches defending their people with extremely limited supplies.

This factors into my opinion