Even if that were true - and it's not - it's simply impossible. The US is entirely incapable of producing all of its own goods. Even if we just accepted that it's going to be a very expensive place for the consumer (again, our costs are WAAAAAAY too high) but it's essential, so let's do it, we can't. Just think about how many laborers are involved around the world in making everything that we consume. We do not have that many unemployed people to put to work on the job. It would require an estimated 63,000,000 laborers just to make the clothing we import. That's just textiles, alone!
I have no idea, as you say, that the world is one big happy place and there's no indication from anything that I've said that I believe that so don't try to make that my narrative. But the world is a big and intertwined and complex place and turning to isolationism is a certain way create insecurity, rather than security. If you want a world where countries cooperate, you're far better off depending on each other for things than shutting each other out (let alone treating others like enemies).
P.S. Despite the fact that people like to say it, the President's primary job is not to protect the people. Now, plenty of Presidents like to twist parts of their responsibilities into sounding like it's all about "do whatever I have to do to keep the people safe" but that's not how the Founding Fathers set it up. How much did you like it when Biden proclaimed and mandated all kinds of things during Covid in the name of "protect the people"?
Nope. Not at all. The point is that we have to rely on others and it's better for everyone involved. China attempted protectionism and isolationism for a very long time a long time ago and they drove a once thriving civilization into poverty. History can be a good teacher or you can ignore it and think you're smarter and that for some reason, this time it'll be different.