The U.N. wants to control the Internet. Specifically, they want to control domain names. U.S. officials say no way thereby guaranteeing that the U.N. won't screw it up.
The U.N. can't even handle humanitarian aid without corrupting it. Look what happened with oil for food in Iraq and sex for food in Africa.
Besides, the U.S. invented the Internet (just ask Al Gore). It's ours.