Companies should be able to make whatever device they want. I use iPhone/iPad when I want to be fairly confident that nobody's actively screenshotting my every move.
The more doors you open intentionally, the more doors become open unintentionally.
If I wanted a device that allows installation of any OS, I would buy one.
Companies like “Honor” are already doing a good job of cloning Apple’s UX. Go right ahead… nobody’s stopping manufacturers from making fully hackable phones.