while i do agree with Tim's argument on privacy concerns, the solution is pretty simple to me: put a giant pop up before installing any sideloaded app. Make sure the user understand fully what exactly they are signing up for: the app could bypass all privacy and security protection set up by Apple, they might pass over their personal information without getting user's explicit conscent and all the scary things. as long as the user knows what are they doing with their devices, this should be fine. And perhaps bury a toggle to allow/disallow sideloading in the setting app under 15 folders or so. It would be a huge headache to me if my mom just randomly brick her phone under 3 taps. this is also exactly why i recommend iPhone to her, as she once asked me where whatsapp was when there were 3 whatsapp shortcuts on her previous Android phone screen. Allow sideloading for tech-savvy ppl, while keep it as idiot-proof as humanly possible.