"Different"

I get it. They want to make sure that someone with a birth defect is not considered of lesser worth. They want to be kind and fair, so they coin labels like "limb different."

I think it rises from the denial that there's a human nature – physical, mental, spiritual. The way they define things, and people, is by their actions. If it walks like a duck and quacks like a duck, it's a duck – nevermind if it needs batteries.

If you define humanity by the things a person does rather than some essence or nature, inequalities of ability are a problem for you. The world's economies define human worth by economic value added, but there's no reason for us to give assent to that. We know better (I hope).

There are normal differences in people, e.g. skin color. There are also abnormal differences, e.g. skin color (albinism). It's normal to have 5 digits on each limb, and rare indeed for more than 5 not to be a defect.

The Salisbury Organist goes to old country churches to play their organs. Not infrequently a note will be bad or the machine slightly out of tune – and you wouldn't be able to tell because he picks the music to fit the organ.

If you don't have a right foot, walking is more of an accomplishment than it is for a healthy youngster. If we flatten everything to "difference" you lose that extra accomplishment.

Plenty of things are legitimately just "difference": including a lot of the skills. Just because it isn't always easy to agree on the names of things that are human essence doesn't mean they aren't real.

We seem to have a hunger to oversimplify. A "definition by action" is very useful (especially in mathematics), while a "definition by essence" is also important in determining purposes – like what a government is actually for. If we don't know what the essence of human-ness is, how do we know what human flourishing is? Keep both approaches, but in tension with each other.