I don't know why people keep comparing iOS to macOS... they are not the same thing.
Probably because Steve Jobs himself said, on stage, that iPhone is running desktop class application software, even saying it was running OSX
iOS (and iPadOS but I'll just say iOS) is a mobile operating system, designed from the ground up to run on a phone. macOS was designed as a general computing OS, which is partially the reason you can install Applications from anywhere.
Explain Android then, because Android is a "mobile operating system" yet it can install applications from anywhere.
Not only that but iPadOS has a desktop mode and can be plugged into an external monitor, albeit with a worse ui and control scheme compared to macOS. (All the more reason I want a macOS dualboot mode for the iPad Pros)
Oh almost forgot to mention, Samsung's builds of Android has a desktop mode on the phone called DeX. Plug your Galaxy phone into a monitor and the UI changes to a desktop format.
So just because iOS is a "mobile operating system" does not excuse it from restricting all software to just one app store. When I can do my taxes and banking and stock trading from my iPhone, it ceases being just a "mobile operating system"
(And before you say "just buy an Android then," switching to the other duopoly also is not a valid excuse and never has been)
But again, people keep making the false equivalency between the 2. What about tvOS? I'm curious as to why everyone makes the argument the want to put any App on their phone when tvOS is sitting there too. Very similar. But I digress.
Whataboutism. We ain't talking about the Apple TV we're talking about the iPhone/iPad.
Sidenote I would love sideloading on tvOS too, as well as watchOS.
The reality is, once Apple is forced to open iOS up, it's going to cause so many new security issues:
1. Apple will be blamed for it.
2. That's all I've got.
Couldn't even finish your "security issue" argument that has been debunked many many times. At that point don't even type it if you can't finish your thought.
Scams, security, instability, battery drainage, all because Apple won't be able to curate the Apps anymore. Again Apple will be blamed and its brand will lose massive value.
THOSE ALREADY HAPPEN EVEN ON THE APP STORE. Gatekeeping iOS doesn't protect you. You can still get infected with malware through websites and you can still get subjected to scam apps on the app store as there's thousands of knockoff and scam apps that app review miss or just ignore
Sideloading: Yes. on a Mobile OS, it is sideloading, because it's not the official way to install Apps. It's a way to get around the security and stability the normal App install process works.
Enough of my rambling and now I'll probably be ripped to shreds
The option to install apps outside of the app store is a choice, a choice you don't have to take when it's enabled in iOS 17. You wanna stay to the app store that's fine. Those who want to install apps outside of the app store can have their choice. There are a lot of apps that Apple for unknown reasons won't allow on the app store, such as retro game emulation or virtualization software for iPadOS. With sideloading, those kinds of apps would be available and the iPad could get even more use. Xbox Cloud and Nvidia GeforceNow for example is available on Android but not iOS because Apple doesn't allow game streaming apps for some reason while Google does.