If your legislature does not listen to you (because you're "not the one in power") then that's a far more serious issue than facial recognition by any metric. If the government is abusing power, that's not the same thing as doing it with the support of the populace, as the 'slippery slope' argument supposes.

Devil's advocate: Why must facial recognition necessarily set us on the the slope to abuse of power? What precedent is there to suppose that?