> had blocked the interstate
There's a permanent roadblock across northbound lanes of interstates in New Mexico (and, I think, Arizona), and across many of the smaller roads in southern Arizona (and, presumably, New Mexico).
> if I'm a US citizen. Then I was free to go.
It also helps to be white, fwiw.
Try driving from San Diego to Los Angeles: there are permanent checkpoints a solid hour's drive from the border — and quite a few non-white residents complain about getting unpleasant levels of attention.
It's not that simple. It's very very hard to travel if the government doesn't want you to.