I think you have a shallow understanding of both free speech and free will if you think this is the gotcha you seem to think it is. Why couldn't people have discussions about free will in a determinist universe? They could be weaved by the laws of physics into having them.

As for free speech online, do you think there should be no limit to what can be said or shared online? What about pedophilia or cannibalism? Or, more relevantly, what about election-denialism, insurrectionism or dangerous health disinformation that are bound to make people act dangerously for themselves and society as a whole? Point is, free speech is never absolute, and where the line is drawned is an important conversation that must be had. There is no easy, objective solution to it.