If the US feels comfortable exterminating Iran over its continued defiance, it will feel further emboldened to threaten anyone who doesn't do what it wants, even over something as trivial as tariffs.

This is the terminal point of "madman theory" and guys like Hegseth and Trump who believe might makes right and they can simply rape, kill, steal, and destroy whatever and whomever.

It's the only real reason the US has the largest military on Earth.

When Trump says he will end "a civilization," he's talking about ours. He's talking about all of it. If we don't capitulate immediately.
America turning itself into "the world's policeman" inevitably means it acts like American police act: as a gang of violent thugs.
NATO was never the reason the US spends so much on its military. When you look at global military spending, you can see this is a US and US only problem. We spend more than the next nine countries combined. We're not spending for "defense." Illegally renaming it "the Department of War" is one of the most on-the-nose things Trump ever did.