You could very easily not install any other store or use any other payment system if you don't want them. You can keep your device 100 % Apple approved even if there exist alternatives. Why take that choice away from others?
> You could very easily not install any other store
But in practice, there are apps we need to use—people who we mostly communicate with over Facebook, movies we want to want that are only on Netflix, etc. In the status quo, we can use those apps, and they're beholden to Apple's guidelines, hopefully reducing the privacy, etc abuses. I can use Facebook and still have some amount of privacy.
In the world where alternate stores exist, I have to choose between using Facebook or having some amount of privacy. Sure, I could not use Facebook, but I'm a real human living in the real world, and that means I miss out on social opportunities that I would rather not miss out on. I—and the vast majority of iOS users, who aren't particularly interested in 3rd party stores—lose a less-terrible Facebook app.
(Not that I'm too happy with Apple here either. Some of Apple's policies are bizarre and abusive, and there are apps I'd like to run that aren't allowed. But I'm not entirely sure it's worth the tradeoff.)
It could fragment the Apple software ecosystem. Since a non-fragmented ecosystem is what I want, I don't like that. Add more stores and my choice to buy into a unified platform is at risk.
Why is fragmentation a problem? There's already fragmentation of the smartphone software ecosystem. How is an app that ships on iOS but not the apple store any different to you than an app that doesn't ship on iOS at all? Either way if you choose to only buy apps through apple you can't get it.
Fragmentation means that many apps I want would no longer be available through a vendor that I trust. No, that trust isn't blind or absolute. Yes, I recognise that Apple's review process is patchy at best—but most developers also fear getting on the wrong side of them and THAT alone has been pretty damn effective at keeping most apps under control.
I'm not convinced this is as big a problem as you think it is. If I chose iOS over Android specifically for privacy reasons I'd be interested in knowing what companies avoid the app store to bypass their privacy restrictions. Do you really want to use a product from a company that would do that as soon as they have the chance or would you rather label them as untrustworthy and find an alternative?
Some apps that would choose to be in the App Store if they had to, would instead use an alternative store. Some apps that wouldn't otherwise exist on iOS, would exist on alternative stores. I'd rather sacrifice that second category to ensure that the first category has to be released on the App Store. If I change my mind, I'll get an Android device. I knew what I was getting into when I bought Apple.
Your choice to buy into a unified platform does not require it to be Apple's unified platform. You can probably find a windows phone and opt into that unified platform.
What you don't get regardless is an apple that "throws its weight around" to force competitors and the like to do what apple wants. That's abuse and bad for everyone. That you happen to like it doesn't make it legal
