As the first sentence of that GPS link points out, the practice of using GPS trackers as a substitute for human agents following cars (which obviously doesn't require a warrant) was halted by the Supreme Court, which stated that the FBI needs a warrant to attach a GPS device to someone's car, not that they are forbidden from using GPS.
GPS tracking was struck down on extremely narrow technical grounds - without a warrant the police do not have the right to trespass upon your vehicle (attach a GPS tracker). They deliberately did not rule upon the rightness or wrongness of tracking someone's public travel without a warrant. Since there will be no physical trespass when airborne drones are tracking our cars, that Supreme Court ruling isn't really relevant.
In my opinion, tracking someone automatically (either via GPS or drone), as opposed to having an actual person follow them, is sufficiently different in terms of cost that it becomes a qualitatively different phenomenon.
> The Preserving Freedom from Unwarranted Surveillance Act would require the government to get a warrant before using aerial drones to surveil U.S. citizens.
It doesn't ban drones. It bans their use for police surveillance without a warrant based on probable cause. A lot of people seem to be confused about this issue.
