When websites and applications are badly designed, they create barriers that exclude people from using the web as it was intended. Poor accessibility creates a disabling environment where the design does not consider the wide variation in human ability and experience. In other words, disability is a conflict between someone’s functional capability and the world we have constructed. In this social view of disability, it is the product that creates the barrier, not the person , just as design is at fault when a site has poor usability.
–Sarah Horton & Whitney Quesenbery, A Web for Everyone