Earlier quoted context omitted.
Don't worry, it won't be legal for Apple to void the warranty for this.
The concern is not a voided warranty. The concern is tech-illiterate users being able to install some random app they found on the web. They find a special version of Facebook and install it, and now their phone is compromised.
The Android ecosystem is a bit of a cesspool, but surely even it isn't having major issues with swaths of people having their phone compromised, right? My parents aren't going to sideload an apk.
I have faith that there's a way to do this right.