My personal perspective, although typing this out I suddenly realize it "doesn't sound very good", but .... I actually think Americans in large part like walls. I'm not saying that's my feeling, just my observation of the country. We like our little separate areas...each state having its own "flavor" and being so beyond-proud of it that it's almost silly (i.e., anyone lived in Texas recently..I have, a couple years ago), the folks in the suburbs love their little areas, people who are more into living downtown and inner city tend to support their little areas, most people IMO live in their own bubble...and like it that way. Leaving it only occasionally, deemed as an adventure.
But it would be next to impossible to figure out where to draw the line, so broad based support for such a thing might never come to be.
We already kind of have this concept with our very different states, which tend to be nationalist [but on a state level] - minded.