If you've nothing to hide, you've nothing to fear, and other similar sentiments:

Actually, when they're observing your behavior, anything you do is suspicious. Not suspicious of a specific crime, but suspicious generally, and they will use this to invoke probable cause and search you or investigate you.

And they will find crimes. Stupid, petty infractions that shouldn't be crimes, but they'll find them. Or if they don't like your social media opinions, they'll make some up.

And they will rob you of any liquid assets (or sufficiently liquefiable assets, or anything else on you they want. And they'll justify it as asset forfeiture. And it will be very difficult to get it back.

So, every citizen has a terrible lot to fear just by being observed by law enforcement. And mass surveillance, such as ALPRs, keeps you in their view.