There is also another video circulating that showed Dr. Dao was clear minded and questioning why he was being asked to leave.  He certainly was not belligerent towards the officers before he was manhandled out of his seat.

Throwing out his background is just chaff to detract from the real issue.  It could have happened to your or anybody else who chose to question why United would remove people who have already boarded and seated on the plane.

United didn't even bother to raise the payout incentive for volunteers to the maximum level before choosing to use brute force.  That speaks volumes on how they view their customers.