I mean that there exists no classifier which consumes as input arbitrary speech, and emits as output a foolproof classification of "hate" or "not hate."

Therefore humans are required to emulate that classifier. Perhaps we call them "judges" or "arbitration panels" or whatever, the name doesn't matter.

My point is that politics will guide the emulation of the classifier, such that it emits results favorable to the loud faction and unfavorable to that faction's enemies.

> I mean that there exists no classifier which consumes as input arbitrary speech, and emits as output a foolproof classification of "hate" or "not hate."

So, that's like every other criminal law ever created.

I do agree this is something bad (for Law in general). But it does not lead to your point that the definition will increase unexpectedly in scope.