I oppose this simply because RU-486 and the Pill can have serious health consequences if misused (for example the extremely high cancer risk if women smoke along with taking the pill, instances of hemorrhaging with the morning after pill, etc.)
I don't trust the average American teen to understand that you can't take Plan-B for every accident, you can't smoke while on the pill, you shouldn't take Plan B if you smoke, and you shouldn't take estrogen abortifacients or other EC drugs if you have a history of certain illnesses or chronic conditions.
In other countries where children do crazy shit like read books and learn in school, teens can be given the responsibility to choose about taking potentially harmful medications. That is the exact reason some drugs are OTC and some aren't.