I have a question about Dumbledore's remarks on the prophecy in Book 6.

If Dumbledore said basically that it was just a prophecy and Harry didn't HAVE to kill Voldemort but he was doing it out of the good of his own heart, why are there even prophecies?

Sorry, I am just really confused.

About R.A.B being Regulus A. Black. In OotP, when they are cleaning the room in Sirius' house, the find a locket that 'could not be opened'. Anyone else think that could maybe be the horcrux Harry is looking for? If so, he'd own it already, which would be a bad thing for Voldemort and that would be a nice plot point for JK.