- If you have at least one alternative to Facebook installed, you lessen their network effect. People now have a choice how to talk to you. (I have another five messaging systems installed myself, but I will settle for everyone picking just their one favorite alternative to avoid a complete monopoly.)

- If you install a Facebook messenger, you know what they're going to do with your metadata. If you install Telegram, you have to be afraid that your data contents might somehow leak in the future. What's better: a definite moderate privacy invasion or a potential worse one? I have trouble answering that for myself, let alone advise others (when it's only between these two and only about privacy).

- Telegram has by far the best UX of any messenger I've ever used. Of course, this is helped by being unencumbered by any and all encryption problems by not having proper encryption, but it sure draws users.