Universal design says build for everyone. Would disability then disappear as a category?

My work is advising NGOs in Amman on accessible buildings, and I keep hearing a hopeful idea that I partly share.

"Universal design" was a term coined by Ron Mace, an American architect who himself used a wheelchair, and a set of principles was drawn up at North Carolina State University in 1997. The idea is simple: design spaces and products so that the widest range of people can use them without adaptation. The classic example is the dropped kerb. It was made for wheelchairs, and now parents with prams, travellers with suitcases and delivery workers use it all day.

Put that next to the social model of disability, a phrase introduced by Michael Oliver in 1983: impairment is a fact about bodies, disability is what a badly designed world does to people with those bodies. If both are right, a fully universal world would have impairments but no disability.

I am not sure. Three doubts:

• Some needs conflict. Tactile paving that guides blind pedestrians shakes my wheelchair. A counter low enough for me is awkward for a tall man with a bad back.
• Pain and fatigue are not removed by a ramp.
• Somebody pays, and "for everyone" can become an excuse to provide nothing specific for anyone.

Is universal design a theory of justice, or good engineering? And would we still need the category "disabled" in the world it promises?