It's not really destroying it. You can still refuse to install any apps not approved by Apple, even if other people do.
It might even be a good test. If Facebook decides they can't be in Apple's store even though the app is free and there is no government pressure for Apple to block it, you might take pause to ask why and decide that you don't want that app.
I already don't use Facebook, but I take your more general point. The main thing I don't want is to feel network-effect pressure from some huge non-Apple platform to install from sources with worse privacy and security guarantees. iOS is so big that effectively no mass-market mobile software can afford to ignore it, and Apple's rules force them to play (somewhat) nice when they show up.
Let's say I did like Facebook, or at least tolerated it because all my family was on it, and chose to use it only on iOS specifically because it was relatively secure and limited their snooping somewhat. Your scenario is a strictly worse situation for me. I was using it and was OK with the situation, now I have to either risk more snooping or drop it. That's not better.
> The main thing I don't want is to feel network-effect pressure from some huge non-Apple platform to install from sources with worse privacy and security guarantees.
What you mean is that you do want app developers to feel network-effect pressure from the huge Apple platform which has those privacy and security requirements. Which you still have as long as a large number of people feel the same and refuse to install apps outside of Apple's store.
It may even benefit you for Apple to have less, but still some, leverage. For example, a third party store might start offering a BitTorrent client for iOS, which Apple only prohibits for bad reasons that don't help you. Then the availability of the apps in another store might convince Apple to allow well-behaved BitTorrent clients in their store to prevent you from switching (since their reasons for prohibiting it are bad). Then you get a selection of vetted clients when you currently have none.
Likewise, if there were other stores then there would be no reason for them to continue their otherwise-useless prohibition on emulators or virtualization.
Meanwhile you could still install all of your apps from their store and they would plausibly still have enough leverage to keep them well-behaved, just not enough to prohibit well-behaved things that you actually want if it's easier to get them some other way.
> Let's say I did like Facebook, or at least tolerated it because all my family was on it, and chose to use it only on iOS specifically because it was relatively secure and limited their snooping somewhat. Your scenario is a strictly worse situation for me. I was using it and was OK with the situation, now I have to either risk more snooping or drop it. That's not better.
What we're after here is a situation where the combination (you, Apple) has enough leverage to cause Facebook to provide an app that isn't ruinously bad on privacy. It's not clear that we're there even now -- Facebook has a huge network effect and basically the only reason Facebook is an app and not a web page is so it can suck up more of your personal information -- but suppose we were. Apple's leverage relative to Facebook is doing you some good.
The answer is then to make sure your leverage against Facebook is sufficient to keep them honest. This could imply some antitrust action against Facebook, e.g. so that you can use an app not written by Facebook to contact your family who uses Facebook, and then choose one willing to meet Apple's standards even if Facebook itself won't. So it's still possible to solve problems like this, to the extent that they exist, through other means.
I just know that these things won't happen right now:
1) Job interview? The big corporate sales prospect I'm courting? "Company policy is that we do all our calls through [some corporate communication tool]. It's on [store that popped up to cater to enterprises, so they could ship more spyware to their employees]" So I cancel the calls, or install that store and their probably-spying app.
2) That chat app or social network your entire family & friend group is on? Crippled or absent on the App Store, full version only on an alternative store.
For #1: "So use a different phone for all business interactions" OK, but right now I don't need to. That is a solution, but right now it's not one I need, and I don't want to need it.
Maybe those wouldn't happen. Right now, they can't. I chose my mobile devices in part for that feature.
It might even be a good test. If Facebook decides they can't be in Apple's store even though the app is free and there is no government pressure for Apple to block it, you might take pause to ask why and decide that you don't want that app.