Letting Russia do whatever they want is arguably not a great strategy towards stopping proliferation, since it sends the message that you're free to do as you please if you have nukes.
I would. But it's true, aggressors rarely listen to reason. They care about strength and about cost. The US didn't withdraw from Iraq and Afghanistan because it was the right thing to do, but because it was too expensive and there wasn't anything to gain. Russia may also withdraw once it becomes undeniable to them that there's no winning this and it's too expensive to continue trying.
There's lots of people arguing for peace talks, and I'd love for that to work, but it won't work if Putin isn't interested in peace, and by all appearances, he isn't. He's made pretty clear that he isn't. The only alternative is to make is aggression unsuccessful.
That's a bit extreme. I'd prefer something in between: stopping Putin but without escalating to nuclear war. Pretty much what's going on right now. It's not great, but it's the least bad option; preferable to nuclear war or genocide.