The comeback would be that obviously people from countries better than America wouldn't immigrate here.
The "you haven't traveled much" comeback also cuts both ways: if you've just vacationed in northern Europe, yeah, you might come back and say well maybe America is not actually the greatest. But if you were deployed in say sub-saharan Africa, you're going to come back and say that this is the best country in the world. The fact is, more of the world is like the latter than the former.
We might be *ed up in a lot of ways, but every single person on this forum is well into the top 1% of wealthiest people in the world, and that says a lot. We should all be thankful to be here.