No, I don't think he should be let to do that, because Ukraine will not be the last country that he takes over. He has already de facto taken over Belarus. Belarus is used as a launching pad for his military operation. Arguably it is no longer an independent country, de facto. All the other post-Soviet states in the region should also fear if the west decides to yield to Putin's demands on Ukraine. There are several countries that are in the line for that. Then it gets to the NATO members, which are probably safe only by virtue of NATO expansion.
On February 28th, 2022. See this statement in context.