It is not an unjust order. Much like a casino, the airlines have the right to remove people from their planes. The only caveat is that they must first solicit volunteers to take some sort of compensation and give up their seat.
As I said before, it could have been handled better. There is no reason for a grown ass man to squeal like Opie on the episode of Andy Griffith where he learns to through a tantrum from his friend.