You absolutely, 100% can't. America has no end of wonderful places to visit, but there are so many parts of the experience of foreign travel that aren't remotely replicated in domestic travel.
Being on the wrong side of a language barrier is profoundly dislocating. A domestic visitor to Big City USA won't find themselves asking for directions in pantomime, they won't have to point at something on a menu and hope for the best, they won't walk into a supermarket and realise that they can't tell shampoo from conditioner. There's a deep sense of vulnerability when you can't communicate effectively, a sense of marginalisation and remoteness.
American tourists have a reputation for assuming that everyone accepts greenbacks. It's a profound experience to realise that the money in your wallet is absolutely worthless to the people around you, that the pieces of paper you sweated to earn might as well be monopoly money to anyone outside of a Bureau de Change. The simple experience of having a pocketful of unfamiliar coins has a lasting effect on your understanding of the nature of money.
True but America is a wide enough place that you can have most of that without leaving the continental USA.
Growing up in Podunk, USA makes people from Big City, USA feel like foreigners (and vice versa). I'm not saying don't go outside the USA (quite the contrary!) but there's quite a bit you can do and see here without a passport.
> I can't help but think that passport ownership is one of the fundamental cultural divides in the US. It's difficult to understand the value of travelling abroad if you've never experienced it and don't know many people who have.
Very true and I don't know anyone that's traveled extensively that doesn't comment on it being a positive experience in hindsight (aside from business travelers complaining about going back to the same places they don't particular like month after month).