Tweaking your wording slightly, it's basically the fundamentals of social contract theory.

I may have the freedom to bash my neighbor's head with a rock, but they have the same freedom to do the same to me. This isn't as useful as the freedom to sleep at night, so we voluntarily give up this freedom.

Reframing to the topic at hand: if the freedom to mutate the code on my mobile device makes it more likely that I'll get pwned by some clever social-engineering than the odds I'll improve my quality of life by tweaking some behaviors on the phone, then it's entirely rational for me to give up that freedom. And, indeed, millions of phone purchasers annually make that decision.