But has it ever been any different? Planting illegal items on people has always been a tactic that the law could use to ruin otherwise clean people they don't like. Talking about mass surveillance being the source of the problem kind of distracts from the fact that we need a solution to this form of abuse of power in general.

Part of the answer is probably constant counter-surveillance of law enforcement themselves (body cams, software logging, etc) stored in an immutable or at least tamper evident data store. Of course, you'd still have a "who watches the watchmen" problem.