Desiring to ascribe reasonable motivations to the carrier, I will assume the limitation on the number of nonsighted individuals is due to the ability of the crew to help in an emergency and perhaps the impact on the rest of the pax in an emergency. Would you have the airline deputize selected passengers to assist the nonsighted? Would you have them bring up reserve crew at the last minute? Should they sign papers acknowledging they are on their own? Could it be that there can be a practical limitation on accommodating a disability? Just my 2c.