Originally Posted by JAXPax

Actually, no. Under the Air Carrier Access Act (different than the Americans With Disabilities Act in a number of key ways, including the always controversial "emotional support" animal definition), there are provisions where the airline must bump other passengers to accommodate a disability. If someone has a medical need for a specific seat, be it permanent disability or temporary condition with doctor's instructions, they must be accommodated as able, and it may mean relocating other passengers from those designated seats. There are other provisions such as if someone wishes to carry their collapsible wheelchair in the cabin, and the primary storage area is already filled, on a narrowbody the airline may have to take a row of 3 coach seats out of service to strap the chair in (most aircraft have a kit on board with lashings and a cover) and treat those three seats like an oversale situation.

So disability is over and above other legal rights and prohibitions against discrimination. For the most part, a qualifying disability trumps everything else (but only must be accommodated in the class of service paid).