I actually firmly believe that leaving Ukraine on its own to be steam rolled by Russia would of increased the worlds chances of a nuclear led extinction event in the near future (10+ years) by a drastic amount.
Think about, Ukraine willing gave up their own nuclear weapons in exchange for promises/pledges/assurances whatever you want to call it really, from multiple countries including Russia that their sovereignty would be respected.
If we don't help Ukraine when that promise is being broken what we are telling all other countries is "give up your nukes and your enemies with nukes are free to invade".
No on one would ever give up there nukes willing again, and nuclear proliferation would go through the roof with every country looking to counter every other countries nuclear weapons.