It's the same logic the US applied to lend-lease, didn't they? There was a good chance of the USSR collapsing until 1943, and you still helped them. Delaying an invading attacker, especially one who may plan, according to their own internal propaganda, to attack other nations later, is already more than "nothing".
The price for peace is living under occupation. Depending on the occupier, this can be a fate worse than death, and significant numbers of Ukrainians appear to think the latter.
And for a very selfish argument: It buys us, the Europeans, more time (with Ukrainian blood) to prepare for war, when Russia attacks the Baltics in a few years. Which we desperately need, as the US will likely break their promise and not help us under the current administration (and who knows who the US elects next).
The 3 years allowed e.g. the Baltics to build extensive defensive fortifications.