Here's a hint: The entire 8M from Parler are using Signal. They're still plotting all the same violence, but instead of being protected by a promise from the founder, they're protected by the design of the app itself. There's no argument to use against Parler that can't be used against Signal. They need to be shut down now, before people die again.
Signal is a threat to our core tenets of freedom, security and democracy. Parler could change its moderation policy tomorrow but Signal can't change how it works.