Surely you see how installing unvetted software on a device that holds your entire life, bank info, photos, etc. probably shouldn't be part of the "happy path" for most people. You shouldn't even install software you haven't fully vetted from the google play store. This should be drilled into non-technical people.
Those of us who want to can easily bypass it. My mom who doesn't know what she's doing and gets a phishing email with a fancy apk attached should probably have a hard time using it.
That means education for people: don't perform actions that are in emails.
Blocking apps is like blocking buying of knifes because one can hurt themselves.
> a device that holds your entire life, bank info, photos, etc
That device was called personal computer for decades, and the world didn't end for the simplicity of installing software on it.
Block installs outside of playstore ON/OFF (ON by default) isn't any less secure. "Sideloading" is scaremongering.
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> a device that holds your entire life, bank info, photos, etc.
I'd see it the other way around and say that a device running an operating system controlled by some company shouldn't hold your entire life, bank info, photos, etc.