While I'm not necessarily disagreeing with that assessment, I think those examples of Gab and Parlor are weak. Those platforms were essentially created and marketed specifically to individuals and groups who were kicked off of other platforms. That demographic will naturally include a much higher proportion of "less than desirable actors".
Many of the largest platforms featured much less moderation in their past - even when they were much larger than Gab or Parlor - while also enjoying a smaller proportion of "less than desirable actors". Of course, whether that level was acceptable is debatable. Free speech is a double-edge sword and moderation is an astoundingly complex problem.
Gab, Parler, Voat, et al are marketed as forums with lax moderation.
The flavors of prejudice that they attract are the direct result of their function. Platforms that start to grow large without controls against hate and other bad actors simply do not continue to grow.
Many of the largest platforms featured much less moderation in their past - even when they were much larger than Gab or Parlor - while also enjoying a smaller proportion of "less than desirable actors". Of course, whether that level was acceptable is debatable. Free speech is a double-edge sword and moderation is an astoundingly complex problem.