If this was a reasonable society, with a reasonable police force: absolutely, narrow definitions of permitted use should be reasonably fine. But the US isn't, and the US doesn't, so in the US, it can't be.
(but then you look at countries where it might be fine, and it turns out that they don't need facial recognition to have a decent enough catch rate, kind of making the whole thing moot. No police force should use it, for wildly different reasons)
Do you want to receive a citation every time you exceed the speed limit by 1 mph? Ever pull off into a parking lot to check your phone or look for something in your car? Trespassing. Ever lose your temper and yell at someone, even briefly? That's assault in most jurisdictions.
Take for examples:
How unimpeachable police testimony is.
How hard it is to overturn a conviction.
How hard it is to dislodge forensic techniques that are known to be bunk.
I could go on. Probably the best correlate we have to this is the rejection of the polygraph and boy in retrospect are we just lucky about that. If King County manages to be the first in such an action against facial recognition they may be worthy of a great deal of praise.
Why is that hard to believe? The article very explicitly and clearly quotes a lawyer who says that is pretty much exactly what is happening.
And regardless, even if there weren't a direct quote from a lawyer on this topic in the article, it still shouldn't be that hard to believe that a computer's output is going to influence the court cases at all. That's not how humans work, for one - people will include everything they 'know' about a situation when making a decision. You can't have a computer producing output and then people ignoring the output and then calling the computer system useful. If people are ignoring the output, then why have the system? And if people aren't ignoring the output, then, the (FALSE) output is being considered in decision-making of which innocent minorities are to be jailed.
It's to prevent some halfwit police officer talking to a halfwit judge and prosecuting some innocent fellow. #donttreadonme