I don't see how that's much better; a judge is just one guy and he's only hearing the cops' side of the story since you aren't allowed to know you've been accused, let alone present your side of the story.
So yeah, there's always the possibility that the cops spy on someone innocent or try to dig up dirt on a journalist or something, and that's why warrants exist. If you don't think a judge's oversight is enough for the police to intrude on someone's privacy, then you're basically saying that the police should only ever have access to OSINT sources and nothing more.