Ancedotal: I used to believe in this "freedom to install". Than my Father got scammed (~$1000) in the name of Electricity recharge. The APK was sent over WhatsApp. Now I am not so sure how to implement this freedom. At the bare minimum there has to be big red warnings. One thing which can immediately improve security is forbidding SMS read access forever. Just like Apple does. No App should be able to read SMS.
So your father: 1. Downloaded a weird file from a stranger 2. Went to the settings and about pyone sceeen 3. Tapped the thing 5 times to activate developer mode 4. Activated installing from third party sources despite the warning there 5. Installed the APK May I suggest the problem is not that this is possible, but a lack of education? If your father is the type that would jump into the bathtub with a toaster because…
In my humble opinion, in the design of a UI or any type of system, kind of have to go where the users take you to some degree. And Android, being an OS for consumer devices, should be geared toward the masses and the mistakes they'll make.