There are parts of our brains that respond very strongly to ritual. As long as they're still there, we might as well use them to impart knowledge that's actually true. Also, if we can't figure out how to supplant religious rituals with new rituals that provide the same social function but without the false beliefs attached, then people will always see a need for religion in their lives.

Edit: Kaj_Sotala wrote a comment expounding the second point above.