In terms of a restaurant, if a patron is refused service before paying, that's different. With airlines, passengers pay up front, and sometimes months ahead. At the very minimum, if someone is kicked off a plane, there should be a full refund, plus compensation for the inconvenience and reimbursement for potential losses that the cost of the ticket would have earned sitting in a bank.
I would agree with Nicolas - if I have paid for a seat, I should get that seat. No buts, no ifs.