Interesting counterarguments are that Gab is not such a place (although Gab has mostly been saying that terrorist attacks can't be planned on their platform) or that in fact the mainstream social media platforms are also such a place and no distinction can be drawn (I actually think there's an argument to be made about how metrics on engagement cause platforms to optimize for outrage and pithy ideology, but I also think that's qualitatively different from what Gab is doing). That the same person had an account on both sites, irrespective of the content they posted, what others posted, and what content the platform encouraged, is not a relevant counterargument.

https://registrarsec.com/

RegistrarSEC, LLC and RegistrarSafe, LLC are ICANN-accredited registrars formed in Delaware and are wholly-owned subsidiaries of Facebook, Inc.