As for the US shutting it down, this is not likely to happen without notice, as there are thousands of aircraft in American airspace using GPS, nearly all as their primary aid, and the US wouldn't forget that.
It hould also be remembered that the aviation segment makes up a relatively small percentage of GPS users. Land users are the most prominent, many not even using the positioning facility - GPS time is used in many applications.
Most of us who know its capabilities, and limitations, accept that GPS works in practice. It would appear that this is not good enough for some, and they are trying to get GPS to not work in theory......
