If Apple allows sideloading apps in any way that is easily accessible to the average user, then
(a) Meta will insist their apps are sideloaded to enable privacy violations. Right now, they cannot say goodbye to iOS users. They could say goodbye to the small percentage that refuse to sideload (or even just put a worse version in the store to those people with enough new features to push most people to sideload.).
(b) Chrome will be sideloadable. Which means web developers will be convinced "sideload Chrome" is a reasonable fix. Reinforcing spiral and soon Google owns the browser in a way that is the envy of 1990's Microsoft. Keep in mind they managed to turn MS's Edge from a third browser to a Chrome skin. That's bad (see Manifest v3, WEI, etc.).
The list goes on, we could talk about Epic and games and store exclusives.
To say nothing about having to debug malware on my family's devices.
