I mostly agree with your comment, having deleted WhatsApp myself this spring. However I have a problem with that.
> many people I know joining Signal or Telegram — the network effect can be broken by being belligerent
Did you not use the same network effect to get people to join Signal/Telegram? While I agree that Signal is morally better (being a non-profit and all), it is still a closed garden, which makes such network effects possible. And this in itself is a moral issue, I think. Personally I would like to use a system like, where everyone can choose his own server. But nobody in my social circle uses it, so I'm stuck with walled gardens...