There are procedures whereby I can be put in jail, removing my permission to leave the room where I've been forcibly relocated. But that doesn't mean I have to "obtain permission to leave the room" right now.
The no-fly list is utterly reprehensible, but it doesn't match what was said.
The CBP is cooperating with Canada to exchange information at border posts in real time about whom to permit to enter or leave over land borders and pressuring Mexico to join. Tracking is already in place. Secret prohibition on leaving by air is already in place for selected persons.
The U.S. government seems to generally support UDHR article 13(2) ("Everyone has the right to leave any country, including his own, and to return to his country") and ICCPR article 12(2) ("Everyone shall be free to leave any country, including his own"). The no-fly list definitely can be a serious problem for this, although people on it often can leave by boat or overland -- though they might have trouble getting the money or necessary visas to do so.
Also, some incidents of investigating and attempting to deport overstays who were deeply integrated into communities and clearly doing super-productive things have led to bad PR for immigration authorities, which could be another reason those authorities are incentivized not to get too good at it (though influenced by factors like what part of the country, where the people have migrated from, what their socioeconomic status is, and others).
Yes.
There are pilot programs at land borders requiring US citizens to submit to exit interviews and obtain permission to leave the country East Berlin-style. Searches on departure are being stepped up every year.
Recently in Atlanta the border cops were stopping everyone in the jetway boarding my international flight for an exit interview and search. They appeared to be looking for money and drugs and asked all of us in plain view to account for exactly how much cash we were carrying before we could be allowed to board. Since the place I was going and Atlanta are both known for petty robbery, I obviously didn't want to answer; the amount I was carrying was under the legal limit but enough to be worth stealing. The border cop was obviously annoyed and insisted on me saying the amount in front of everyone.
As long as police agency budgets shoot skyward and Americans are happy to submit to authorities, the sky's the limit.