Only physical practicalities will prevent this thinking be applied throughoutly: we can't have guardians preventing people from being scammed face to face. But having to identify yourself on a desktop computer and only be allowed to install software vetted by Microsoft and bunch of governments is readily on the books for the kind of thinking that makes these suggestions.

That's where it inevitably leads to. If people can't be allowed to be responsible for X, next they can't be allowed to be responsible for Y, then Z -- all for their own sake. Google taking some mythical "responsibility" on behalf of their users means the users are left powerless and that is that something Google wants more than just being a "good guy" who protects people from conmen.

It's not like people simply couldn't just limit themselves to installing apps from Google Play already, without these "guardrails". Android currently does make it clear that installing unknown apks from an external source is risky and shouldn't be done unless you really, really know what you're doing. No further technical solutions are required for the problem. You can't fix stupidity with technical means.