That's awful, but it has nothing to do with sideloading or needing locked down phones.

Apparently this idea that security and user control are a trade off has been sold pretty well, and it's bull shit. Nothing about a phone which isn't locked down to the user precludes all the security features you'd want on by default for your mother.

But I doubt you'll catch Apple or Google going out of their way to explain that. They're better off having you believe that the trade off is necessary, and you probably wouldn't miss the freedom anyway.