Nothing about paying for a service disallows the airline company from putting cameras in the public space they operate for a profit unless it's specified in the contract that they are not allowed to do so. I guarantee you they did not put restrictions like that on themselves in the contract with the customer. Your argument that cameras did not exist in these spaces 20 years ago is completely irrelevant to what the airline can do now. If you don't like it, get the laws changed. By this reasoning, the airport itself could not put up security cameras beyond the security checkpoints where only ticketed passengers are allowed. That's absurd.