I don't even want to hear about free speech. You aren't entitled to someone else's attention. Trolling is not a Constitutional right. You want to do that, spin up your own instance.
And certainly, someone could start a free-speech-anarchist instance with all pest controls off. For mastodon.social, though, I think they have a real responsibility to crack down on this shit.
The right to abuse is not about freedom. It silences people. It restricts freedom and expression—it never enhances it.