To me, ADS-B reminds me of EZ-Pass. Both were government programs that sold themselves as a convenience to the public.
In the case of ADS-B “Out”, the government got better air traffic control abilities, and the “In” gave the public weather and traffic visibility.
EZ-Pass, for those who don’t know, is a transponder that is carried in a car that is used to automatically pay tolls. The government gets better/easier toll collection, and the travelling public gets the convenience of not being stuck in toll-booth traffic.
But, just like with ADS-B, the EZ-Pass transponder is a defacto tracking device. And it would be extremely easy for the government to see if someone was speeding by simply checking the travel time between two toll boths. The government realized that if they did this, NO ONE would sign up for EZ-Pass. So, as far as I know, it’s forbidden to use EZ-Pass data to issue speeding tickets.
It seems to me the same restriction should be applied to ADS-B. The only allowable use should be for its primary purpose of safety, such as air-traffic control and collision avoidance. Any use for enforcement or revenue should be disallowed.