The lack of a social network is why I settled on Signal. Before using Signal I tried Telegram, which requires a phone number and if they recognize your number in any of their user's contact list (which many people seem happy to allow access to), they'll send them a notification telling them their contact has joined. I got a nasty message within 10 minutes of making an account from a woman accusing me of pretending to be her deceased father. I had inherited his phone number a decade prior, and it told her I had made an account. I was so shocked they not only allowed, but encouraged such behavior that I deleted it promptly and swore I'd never use it again.
>>aquova+(OP)
Signal does the same thing. Or maybe it used to but they changed it. I have a bunch of notifications of "so and so is on Signal" from when I joined years ago.
Can't say I've ever gotten any psycho responses from it though.