So far, I have yet to hear of a safety reason aired for their removal.
The airlines only need a "perceived" safety reason... such as suspicious behavior. The airline doesn't actually need to be correct in its assessment of a safety risk.
As long as the airline's decision has a
rational basis for safety and it is not arbitrary or capricious, it will be deemed an appropriate action.
However, the discretion of the crew, although broad, is not unlimited. Although the crew can remove a passenger for suspicious activity, the law does not provide
absolute protection to disclosures of suspicious activity. For example, if a crew removed a person because another passenger told security personnel,
based entirely on the passenger's race, that the passenger was dangerous, this would clearly be reckless as to the truth or falsity of the statement and would not sheltered by the law. If, however, the decision by the flight crew was not arbitrary or capricious, then the actions will be appropriate.
This is what the case will likely turn on if it is not settled: Whether they were removed solely on the basis of race, or was there a non-arbitrary or non-capricious safety reason, such as abnormal and suspicious behavior, that led to the removal.