Everything is insecure for the user. Google, Apple, Windows, knowingly includes apps with features that is ignoring your privacy. So “insecure” is a wide topic, we’ve accepted to debate only in certain narrow areas. F-Droid makes people a little more aware.
I don’t mind paying a fair price, for a service, so they should go for it. I use both Signal and Telegram, and I would pay for Telegram too, if the price was more fair…