Would a camera on the flight deck deter someone who wanted to crash the aircraft? I think not.
If you're going to fit cameras to the aircraft then how about a set looking back at the wings, engines and tail? I'm sure if you stored video from them, as well as making it available to the flight crew, it would assist accident investigation far more in cases of structural failure. If the crew could see nasties such as significant leading edge damage then they'd know not to slow down too much and incidents such as the El Al 747F at Amsterdam could be avoided.