Thankfully the App Store doesn't allow side loading, because it completely stops fraud like this. At least that's the number one reason why I keep getting told if we allow side loading this will happen.
But most reasonable people agree there's no tangible use case to not wearing a seatbelt. There are infinite tangible use cases to using software outside the app store, that reasonable people can all acknowledge.
Also they should check the app but wallet security is tricky - you can put subtle vulnerabilities in that are hard to spot.
I think the actual problem is with how the App Store changes the way people think about and relate to software. The fact is, running code on your computer is dangerous. You are trusting it with control over its operations. The responsible thing to do is provide platform-level safeguards (permissions systems, sandboxing) and engender a general understanding that you should only run an app vetted by someone you would hand your phone to.
This is fundamentally incompatible with software as a market, of course, so this path will never be taken.