Importantly, "free speech" is about government, not privately owned spaces.
We believe the government should not be given the power to censor speech, because people are born into it without a choice. Governments could use this power nefariously, and their citizens would have no meaningful recourse.
Nobody is born into Reddit or kbin or Lemmy. If someone doesn't like the rules of a given instance, they are welcome to leave and free themselves of this burden.