You may disagree with those limits but they've always been there.
[0]https://en.wikipedia.org/wiki/United_States_free_speech_exce...
Meanwhile, cultures differ, and people outside of the US may well see their own governments' drawing the lines elsewhere, for instance banning of hate speech and Nazi propaganda, as "absolutely necessary."
Yes it does. That's what subjective means.
Obviously, many people refuse to accept that their personal opinions on political matters are anything less than absolute, immutable, objective fact, but that isn't relevant, because refusing to accept that doesn't make it, or you, objective.
>Even mathematicians have differed about proofs.
Politics isn't math. There is no equation or statement that can quantify the American model of freedom of speech, nor prove it correct, much less more correct than all other models, in the same way as E=MC^2 or Pythagoras' theorem.