Shooting the hostage does technically end the negotiation, and that’s the equivalent to what he is suggesting
The only hostage in this situation is Ukrainian population, that is slowly getting butchered.
So in your analogy, he is the only one negotiating the release of hostages, while everybody else is busy killing them.
cede territory
Lots if not most of people would prefer to be alive on ceded territory than dead on whatever territory. You are suggesting to kill millions of innocent people without giving them a meaningful choice.
selfish asshole
Do you think millions of people who will get to live due to his actions are going to call him selfish? I wouldn't.
If what you mean instead is that his actions wouldn't benefit USA in its geopolitical game with Russia by the cost of lives of other people - you can just say that.
There was a highly upvoted post here on lemmy with "saving lives is hot" as the title, what happened to that? Or does it work only when it is about Americans, and Ukrainians can be massacred?