Don't install random shit scam apps then. It's easy. Just don't do it. Use the App Store. Just because you trust them doesn't mean the entire userbase should all be forced to trust Apple and only Apple.
I have my popcorn ready for the new wave of installing malware apps through some click jacking scams.
Again, Apple already allows grannies to be scammed with apps right on the App Store. Apps which are advertised by web popups that try to stop you from going Back, and throw up "You're INFECTED!" warnings and alerts. Then they route you to the App Store to get the scammy apps, with often weekly subscriptions. Apple routinely lets these listings stay up for a long time. I can see an app right now called "Storage Cleaner_ Phone Cleanup" It charges victims $9.99 a month to pretend to do several things that the OS already includes as features. And another one called "Phone Guard: Secure Cleaner" - same basic deal, $6.99 a week.
The sandboxing should be what keeps us safe from "malware" -- these apps don't have root. They can't access your phone's contacts without explicit permission, nor take control of the radios, nor replace your system apps.
Apple can't or won't keep people safe on the App Store. But they still use this line about the poor confused grannies and toddlers as an excuse of why we have to let them keep 100% control of every iPhone in the world, in a way that just happens to earn them tens of billions of dollars every year.