Clearly NASA & FAA know a lot more than you and most of us do. If they choose to let SpaceX continue launching their rockets, there must be a good reason behind it.
Unlike the Shuttle, SpaceX's manned vehicle will have the ability to escape an exploding launcher. It's best avoided, obviously, but a repeat of Challenger should end with everybody safe and sound, just not in orbit.
Because rockets explode all the time and it's not really dangerous unless people are involved. Rockets are routinely exploded on purpose during testing.
