[mmoche]

Those in a position of relative power (e.g. airline employees) are not allowed to ask "what disease do you have that merits this animal?" but they are allowed to ask "what services does this animal provide?" There is a clear and obvious distinction between those questions, and the answer to the second question will clearly identify those who require exceedingly well-trained and expensive service animals. People who want to carry their dogs onboard without paying a fee are less likely to have an answer.