As a frequent flier in and out of Tucson, I am aware there is a much deeper issue with the airlines than the forcible removal of a passenger from a United Airlines flight.
Airlines exist to make money; all else is secondary. You may be well treated if you pay full fare, or fly business or first class. All other passengers are simply an annoyance to the airline.
The airlines have been abusing passengers for years, though it rarely reaches this stage of physical violence. This is the only industry that routinely punishes its customers. Fees as high as $250 to change flights, add-on charges for baggage, food, blankets. Increasingly cramped and uncomfortable seating, and disappearing customer service are the norm throughout the industry.
The airlines merged to avoid the possibility of competition on routes. With no meaningful government regulation of corporate behavior, the airlines will continue to treat customers with contempt. We cannot build an effective, convenient and fairly priced transportation system with a for-profit approach.