Well, duh, this is sort of the paramount point and the reason this is a really bad idea.
To those who say, "well, YOU don't have to use a third party app store, so what are you worried about?", you further miss the point. We share significant amounts of content between friends and family. So my contact information, shared photos, contents of mail and text messages, and more, reside on my wife's, kids, and friends phones (all iOS) There is a greater level of trust to do so given the intrinsic security of the shared ecosystem. So it "someone else" starts using unvetted apps from a third party app store which does a lot of harvesting, you are indirectly harmed even if you yourself do not use a third party store.
For those that do, how does Apple address the aforementioned "security assurance and privacy protection" by allowing unvetted apps on the store? Do they allow unfettered access to all API's/tools/data? Do they cut off access to Contacts, Wallet, Messages, Mail, Photos, Files, and more to try and protect the ecosystem? What becomes exploitable by allowing a "front door" into iOS for third party app stores?
I don't think many people think about the ramifications of this, and more fundamentally, this is product and feature of the Apple's / Google's businesses. To what level do we want governments, including unelected regulators, putting their hands on the wheels of free enterprise, innovation, investment, customer relations, and success? It is a very dangerous manner of thinking.
And where is there a vast majority of users even complaining about this? These is no cacophony, not barely a whimper... Most people are fully aware of the ecosystem, enjoy it , and feel well served and protected by it.
Let others innovate a better solution/ecosytem in the open market.
