Bruce Schneier links
to this article
about a plane between France and Mexico being diverted because a
passenger on board was on the US no-fly list and the plane would have
gone over the US. I agree with Bruce that the no-fly list is
basically stupid, but once you accept its premises this strikes me as
not entirely crazy. If your concern is that someone is going to hijack
the plane and crash it into a building, then he doesn't even have to
land to do that, just get close enough to the target that it's hard to
know what's up and divert him. So, with that reasoning I can see why
you would think that it was undesirable to even let him into US
airspace. Moreover, it has the side benefit of letting
TSA look like they're really trying hard to keep you safe,
while (mostly) only inconveniencing foreigners. What's the downside
from their perspective?

A passenger on a plane who has passed some reasonable ground security and would be pummeled to a pulp if he tried to take over the plane is not a security threat. Quietly land the plane at its destination and put him on a plane back to his/her country. Other countries manage to do this every day without an issue. The hijacking of passenger planes is no longer an attack vector.
And what is the downside? "foreigners" opinions that the TSA is a bunch of unthinking thugs will continue to be reinforced.
(for the record the TSA has improved incredibly over even the last year - but the checking of ids and the no-fly list is not an risk mitigation)
Well, recall I did say that I thought the whole thing was silly. My
point isn't that this is a good idea, but that there is some set of
(wrong, IMO) assumptions in which it would be.
As for foreigners opinions about the TSA being negative? Are you
sure TSA thinks that's a bug?