I think when speech starts to risk real harm to others, we need to start thinking carefully about it. It's not so clear cut, but I think that if someone threatens to harm someone with some degree of seriousness, society should be able to act before that harm occurs.
With Parler (and to be fair, Twitter), I see it creating more radicalization, which very directly creates a risk of harm to others as we saw play out on the 6th. And I don't think we should tolerate it, or we're stuck just treating symptoms rather than causes.