The software developers and software companies of today are on average not to be trusted: they will outright steal the customers' private information and sell it or give it away without a second thought.
Absent adequate laws, the success of the iOS permissions model and the complete failure of the Android permission model in protecting customers is perhaps the clearest proof of what a sandbox can achieve. I am reasonably sure that I can download an iOS app - any app - and that my private information will remain secure.
The platforms of today must offer a secure, privacy-preserving running environment. The free for all is dead, and it has been killed by greedy devs and companies.