The reality is different.
First, Apple already offers at least two ways to sideload apps, which perfectly safe.
Second,the App Store is already full of scamsand junk.

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The report seems timed to counter thelatest anti-trust procedures and investigationsin the EU and the US.
Apples report paints alternate app stores as wretched hives of malware and scams.
But this misrepresents the reality.

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Sideloading is already possible.
One way is viaTestFlight, Apples platform for third-party developers to distribute beta apps.
Another is Enterprise Certificates, a method for big companies to distribute proprietary in-house software to their employees.
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For the reality of sideloading, look at the Mac.
Any developer can submit their app to be notarized, and it can then be used on the Mac.
It is, then, entirely possible to safely sideload apps on the iPhone and iPad.
This notarization process would confirm apps still complied with Apples ever-deeper privacy protections, for example.
The only part Apple would have to skip would be taking its 30% revenue cut.
The Risks
Thats not to say there arent risks in sideloading apps.
Apples notarization process would not block a game designed to milk money from children via in-app purchases.
Meanwhile, scam apps already manage to evade Apples App Store review process.
The answer may not be third-party app stores, but the current situation is far from ideal.