Keep in mind that Android has like a billion users who have never touched a Windows computer. (And unmanaged Windows was/is also a disaster zone.) Coming at this from a internet forum perspective is missing the scope of the problem.
> I'm fine with an opt-in lock-down feature
Me too, but it's really just some UI semantics whether this is 'opt-in' or 'opt-out'. Essentially it would be an option to set up the phone in "developer mode".
Not really. With opt-out, if I buy a new phone or even just reinstall OS, I will now have to wait 24 hours before doing anything useful with it.
There is a big difference between opt-in and opt-out that isn't semantics. You can't slowly discourage, deprecate and delete the default the way you can an opt-in, because too many people keep using it.