From what I can tell, The Independent article was not sourced from an expert either so your attempt to show that the Independent article has more "weight" does not back things up.

Here's an article quoting an aviation attorney: http://www.philly.com/philly/columnists/stu_bykofsky/United-...

  "Under certain conditions, airlines can bar passengers from boarding - if the passenger is unruly or intoxicated or on a terrorist watch list - but United had no right to remove Dao, says aviation law expert Arthur Wolk, a Center City attorney who read the 45-page “contract of carriage.”

  Wolk says Dao “absolutely” had the right to the seat, and this was not a case of “overbooking,” he says, because all the passengers had seats. What happened to Dao was “assault and battery,” he says.

  “There’s absolutely no humanity left in the airline business,” Wolk says, adding that United routinely finishes low in surveys of passenger satisfaction. “I would sue their asses off.”

  Is there any question that Dao is going to sue?  John Banzhaf, a professor at the George Washington University Law School, agrees with Wolk’s analysis. He says United is “citing the wrong federal rule to justify its illegal request to force a passenger already boarded and seated to disembark.”"