Discrimination? Or prudent protection against ourselves?

Over at Oxblog, Josh Chafetz thinks that the Constitutional provision requiring that only native-born Americans can be President is discriminatory, stupid, and in need of amendment.
I disagree.
Consider the history of the Western World up to the time of the Founders. How many countries in Europe were ruled by non-natives, including not just countries that might have been conquered, but countries whose rulers had been invited to take the throne (William and Mary of Orange who were invited by the English Parliament to come from the Netherlands to be King and Queen, vice the papist James II, come to mind). Certainly their late nemesis George III was almost more German than he was English.
This provision was put in the Constitution to protect us from ourselves and force us to rely on no other nation to provide our Chief Executive and Commander in Chief. It has nothing at all to do with people who immigrated here when they were two and have lived here as naturalized citizens ever since. It has everything to do with keeping adult foreigners from taking (or being given) citizenship and assuming the Oval Office.