That's not a good argument against ALPRs because citizens can theoretically set up an ALPRs too.

True, but I’d imagine if a few techies in the community setup an open-ALPR network and started a website “where is the police chief and all his family vehicles .com” that the police department’s views towards the free and open use of such data without a warrant would change quite quickly. So long as that data was only collected on public streets it would be perfectly legal.

It's already prohibited in a number of states and I'd bet that if citizens tried to do that at any scale, then laws would be quickly passed to make the state and its corporate partners the only ones allowed to do so everywhere else.

And do! A lot of newer home security cameras have ALPRs so you can set up rules like "if a car with a plate number not on this whitelist pulls up on my driveway send me an SMS"

"we weren't allowed to use equipment that wasn't common for normal people to use."

Is it common for normal people to set up and use ALPRs?

Citizens can theoretically use long-distance microphones too. The criteria is whether they commonly do, not whether it's possible.

I actually have set up a few! On my property, not every major intersection in town, though.

a single person can't set up a fine-grained nationwide network of cameras with a unified search interface that lets one track everyones daily movements.