So just hand the data right to them?
"I'm more concerned about Facebook/Google/Microsoft/Apple tracking me, reading my private conversations, and selling my data to the highest bidder."
End-to-end encryption is the only solution to that problem. Open source software and decentralization is nice and all but to become a mobile app it'll have to be compiled and run on a closed platform and will almost certainly use APIs of that platform.
I don't want something that is perfectly secure, I want something I can run on servers I control, so that every message I send doesn't go through, and be stored on, servers controlled by the big four.
TOX is a great example, as all the services like this try too hard to be perfectly secure, rather than trying to be user friendly. Most people just want something that lets them easily message their friends, and are willing to sacrifice privacy (quite possibly because they are oblivious to it) to have that.
Even OTR + ICQ/AOL/MSN Messenger were better than what we have now in terms of security and privacy, but people gave those up for simplicity.
That's not necessarily true. End to end encryption doesn't need to be a compiled mobile app or send messages over a closed platform.
We built a decentralized, open source, freely distributable, browser-based Twitter client utilizing end-to-end encryption at www.seecret.io specifically to address that.
Presently, mobile devices aren't (effective) general purpose computers. That must change.