I think parental controls are more about the parent(s) feeling good about themselves. Most probably realize they can't stop their kids from seeing this stuff one way or another but if they are proactive and enable parental controls they can feel like they did everything possible to prevent it.
Really? Enabling parent control on the iPhone blocks both Safari and Opera which means no access to wikipedia and other amazing sources of education just because they may stumble on porn which can be found everywhere anyway? There's nothing to feel good about this. In the meantime, I guess the iFart app is not forbidden, it looks more like "dumbing down kids" than "parental control" to me.
It's not about "dumbing down" kids at all. How many kids are accessing the internet exclusively via an iphone? It's a lot harder to monitor internet usage on a 3.5in screen that can be held in the hand than it is, say, a 17in monitor in the living room. I'm all for letting kids have internet access. I'm also all for monitoring it. You can't do that effectively with an iphone. Sure, kids should have access to the internet, but they don't need it on every single freaking device under the sun.
