So why can't an adult install a porn app, to use this lame red herring? Why can't there be a parental control giving the parent the decision of whether or not t

So why can't an adult install a porn app, to use this lame red herring? Why can't there be a parental control giving the parent the decision of whether or not to install porn? Why couldn't there be an alternative to the App Store, where you can buy a porn app, but simply have a parental control to disable access to apps not from the App Store? The power over the decision of which content is appropriate lies with the parents, not with the platform vendor.