As I said these issue already exists with sideloading and private App Stores. Some of those issues are alleviated with the OS model, which simply doesn't allow

As I said these issue already exists with sideloading and private App Stores. Some of those issues are alleviated with the OS model, which simply doesn't allow to change the search engine and install keyloggers. If someone chooses to leave the App Store and be vulnerable to issues such as sex ad notifications and secretly uploading photos the issue should be how it's communicated. I haven't used an Android device in a while, but the last time I used one it was a simple dialog and you could install whatever you like. On the Mac you have to open the settings and permit every unsigned application if gatekeeper is active. Something like this seems like a reasonable solution.