Resistance to a policy that asks pre-boarders to remain seated till others deplane seems to be motivated by the feeling that people with disabilities suffer enough and are entitled to be accommodated more than equally to compensate for it. It wouldn't be viable to enforce such a policy, but announcing it would help dissuade some who pre-board just to get a better choice of seats. Some handicapped people also believe that nobody else should use the handicapped stalls in the restrooms when there is no handicapped person present, just in case a handicapped person might show up and have to wait a minute. The ADA law is supposed to require reasonable accommodation to provide equal access, not better access.