Bad solution: disallow this entirely.
I'd still put that as a bad solution. It is necessary but not sufficient for the owner of a device to be be able to run arbitrary code. It also must be the case that nobody can prevent the owner from running arbitrary code on their own device. The infrastructure required for Apple to be the intermediate for enabling such a feature would mean that Apple could also block the authorization from going through.
In effect, Apple must not be in a position to perform a man in the middle attack between an owner and the owner's device.
iOS developers are sideloading their apps hundreds of times each day...
(Accounts that were inactive from publishing apps/games to the store. The accounts may have well been “active” for side loading/dev work)
Why isn't it free, or a nominal one-time $20 fee like the Microsoft Xbox developer program? Very good question.
Exactly. Want to sideload MAME? It's not a big deal. Go to https://github.com/yoshisuga/MAME4iOS and follow the "Building / Installation / Sideloading" instructions.
(And what if you don’t own a Mac? Create an entire macOS VM just for the purpose of installing an app on your phone?)
Compiling source on anything other than MacOS (at least was - not looked into it in a while) a PITA.
And to take the argument more broadly: how many of us here on HN became interested in computing because they screwed around on their PC as a child? What about today's children, who get a smartphone, a tablet and maybe a Chromebook? What are we teaching them?
I am for hassle-free side loading on every platform (Even on games consoles). I also dislike how most smartphones and tablets have become "Internet consumption devices".