They don’t need to be protected from nudity in and of itself. However if they are talking to an adult or a stranger randomly messages them, it would be nice if the device blurs pornographic imagery.

If they are looking for porn themselves (e.g. are of the age to care for such things), they can download it themselves via Safari.

But generally speaking there’s no need to trade this stuff on iMessage.

This is precisely what I meant by pointless: outside of 20somethings and certain locales (particularly large cities), alternate lifestyles exist where parents simply may not want this for their children.

I'd suggest arguments for or against any particular culture or lifestyle, or attempting to deny they exist, exceed the scope of discussing the feature itself.

They're being protected from the abuse of their nude image by online contacts.