If my kid someone ordered a cellphone without my knowledge and got it shipped to my house and opened it and set it up, I have a lot bigger problems than him finding sex or "wrong" political opinions on that phone.

While I know some people at HN would still be mad if the App Store defaulted to "kid safe," it's a fix with much smaller side-effects than outright bans. Assuming "to protect the kids" is really the motive.

Now suppose that clueless suburban soccer mom got her kid an iPhone and doesn't [want to] know anything about configuring this device. Box arrives, she hands it to the kid.

Yes, this parent has problems. And it's this situation that Apple thinks they're watching out for.

Then the kid stumbles across adult material on his new fancy phone, and is apparently scarred for life.

Oh wait, this already "happens". The phones come with webbrowsers.

So set it to "child-safe" mode by default, and require a credit card or other age-verification mechanism to unlock it.

I really don't understand what problem Apple is trying to solve.

Cynically, I'd say Apple is (successfully, judging by the commentary here) solving the problem of finding reasonable-sounding justifications of their app store approval process (and the inevitable arbitrary decisions that come with it).

They're trying to avoid the situation where they have to stand up to a morality-in-the-media-type group and defend someone else's freedom of expression.

Allowing the web is PR-defensible: "it's the web". But when it comes to things you explicitly review and choose to allow in your store, you're forced to either stand up for adults' right to that content, or you preemptively censor yourself and your suppliers. (a la Walmart)