'Disability' - good. 'Handicapped' - bad. Why?

On friday to disability awareness workshop. Semi-compulsory, and very useful, couple of hours discussing real problems and possible solutions. So let's get that out of the way.
But the the strange insistence on the term 'disabled' provoked a question:
'Why is disabled not insulting, in spite of the fact that it's an absolute term, and 'handicapped' IS in spite of the fact that it's a relative term?
Answer from the workshop leader:
'Because it is the image of the person going Cap-In-Hand for discretionary charity instead of getting what is theirs by right. It's an image of philanthropy' (I'm tidying up a bit.)
Which is of course nonsense. As anyone who's ever lived within half a mile of a betting shop or watched saturday afternoon TV or who's father caught a bus to work will testify.
I checked the derivation of 'Handicapped'. As well as the current horse racing usage, it possibly came from an old game of chance: 'Hand in Cap' - a sort of lucky dip game which has been forgotten for a very long time. Anyone heard of it?
Nothing about charity or the classic C19 patronisation of the disabled.
It sounds to me as if a few uncool professionals thought that the word SOUNDED like 'Cap-in-hand' - a bit like the Mormons who tried to sue Led Zeppelin because when you listened to their records backwards... And thought they would make an impression by dicouraging its usage.
With enough dissemination, this becomes a fact. So that now, wheelchair users or the blind will genuinely feel affronted if they are referred to as 'handicapped'. Even though they have no idea of the derivation, and even though that word is much more sympathetic to their aspirations than Disabled. Which means NOT ABLE TO as opposed to NOT BEING ABLE TO DO CERTAIN THINGS, OR CERTAIN THINGS AS WELL AS SOME OTHER PEOPLE, or OR CERTAIN THINGS AS WELL AS SOME OTHER PEOPLE UNDER CERTAIN CIRCUMSTANCES. Like a racehorse carrying a weight.
Surely that is a much more positive image than 'disabled' - which suggests a clamped Ford Escort or a broken light switch. No use to anyone. In fact, looking at it coldly, 'disabled is almost as bad as 'in-valid'.
Maybe it's time to rethink the whole notion of physical capability in this era of in which a person's power depends on the skilful use of a computer.
I suspect most of our definitions of what it means to be 'able' are hangovers from the age of steam, when physical and sensory capacity were essential in order to survive.
They were obsolete throughout the electrical age of the C20, and they are possibly even a definite handicap to the age of new technology as they inhibit the full exploitation of the skills base.
So maybe we don't need a categorisation any more. Or at least until we have made categorisation uneccessary by ensuring access to places of work for EVERYONE with skills to exploit. Not just those who can see or walk, for instance.
Then, the productive capacity of the workforce will not be inhibited by mobility or sensory deprivation and defining terms will become uneccessary.
But what would be the political implications of a non physically hierarchical society?