I get the feeling that the people who invented the "One child policy" where at a different stage in civilization/education/whatever you call, than the people for whom they made the rule. So they didn't even consider that the public might choose to get rid of their girls.
China has been extremely focus on reaching the western standards of living, but their culture haven't been able to keep up. I think it's great that they addressed the issue of over-population, something that a country like India has failed to do. Their error was that they didn't try to bring about lower birth rates though education and welfare programs and instead opted for punishment. The Chinese where given an incentive to abort girls, so in hindsight it's not a surprise that things have worked out the way they have.