> - Block only sites that state they are adult.

This is the problem. What is an "adult" web site? Websites that show porn? Websites that show gore? Websites that show violence? Websites that show non-porn naked people? Websites that have curse words? Websites that promote cults and alternate religions?

Why is it the site's responsibility to "state" that they are adult, given whatever parameters they dream up? Why is it the government's responsibility to say "This is adult content, but that isn't adult content?" Shouldn't the parent get to decide which categories of content count as "adult"?