>I'd be interested to see if opponents of mass surveillance could draft good legislation to curb potential abuses

Isn't this just warrants? We have infrastructure in place, if police have reasonable suspicion a crime has occurred, they go to a judge and convince them they have enough evidence and the judge gives them a warrant. The problem is police and Flock are constantly arguing they shouldn't need a warrant to use the data, and it creates a system designed for abuse.