Presumably, if those friends - or merchants, or colleagues - don't want to change operating systems and throw away their device and all their apps, you should just stop talking to them:
https://finance.yahoo.com/news/tim-cook-says-buy-mom-210347694.html
One of the clinical signs that someone is in a cult is that they are encouraged to isolate themselves from people who aren't also in that cult:
https://en.wikipedia.org/wiki/Isolation_to_facilitate_abuse#In_cults
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But there are billions of Apple customers and only a small (but vocal and obnoxious!) minority of those customers are actual cult members, which means that there are billions of people who'd prefer to have private, secure communications with everyone in their lives, not just their fellow Apple customers.
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