You are missing the point. It isn't about USA being able to shut GPS down for Europeans. They already can, and that's pretty natural, because it's their military system in the first place. It isn't about being able to shut Galileo down as well. It is about EU knowingly building the system (using their money) that can be used by anyone, but can be shut down without shutting down GPS (which is capable of limiting availability to USA military forces only, should they wish so), because one particular aggressive country threatened to use violence otherwise.
As I understand, it's not that America can call Europe and say "Shut down the GPS", it's that America wants to be able to jam GPS (which is reciprocal, BTW. Europe can go to war now and jam GPS signals).
It's quite reasonable that if a third-party is supplying weapons to an enemy, it gets caught up in the cross-fire.
