I don't care if it is legal or not, I feel an airline is obligated to a minimum standard of accommodation. If you felt your health would be endangered, and endanger even remotely the safe operation of the flight, I think you are due a modicum of accommodation, including the ability to at least standby for a later flight or different routing.

Which contract airline operates JAX-ORD? (This may be obvious to some, but my UAX experience has so far been limited to SkyWest.)