You seem to be under the impression that you have any rights on an airplane. Really, you have none.
You are required by law to listen to the stewards and obey them, your movements on the airplane and where you are flying to are restricted by law, your presence on the airplane is restricted, your speech on the airplane is restricted, any semblance of privacy are out the window as soon as you walk on the airport property. I could go on. Now, these are all by the government. On top of that, you have the rules of the airlines. It's their plane and they can do what they want with it, including who they decide to carry on it.
Well, the airlines are common carriers, so they have to publish and follow "Conditions of Carriage", and they can't refuse to transport anyone who meets those conditions.
But there is typically a condition that covers this case, i.e.
Persons who have an offensive odor, except where such condition is the result of a qualified disability