I watched the video - clearly the passengers sitting around the woman being ejected from the aircraft witnessed what happened and were quite disturbed. The agent who had to ask her to leave was only doing her job - that fact was recognized by the ejected woman. Obviously, the video didn't show the precipitating event, but in the many decades I have been flying, I've never seen passengers rally behind another passenger unless they genuinely thought the person had been wronged. American really needs to investigate this matter and take appropriate action against the male attendant if warranted (the 8-10 people sitting around definitely think it was). On airliners.net it is reported that the incident occurred on October 11 on a flight from from ATL-PHX-PDX. Should be very easy to identify both the ejected passenger as well as the attendant.
This is really an unfortunate incident for American - lots of customers will see this video and book on another carrier in the future, if only in solidarity with someone they believe was wronged. The airline really does need to 'make it right' for its own sake, irrespective of who was 'right' and who was 'wrong'. Bad showing.