Some very disabled people obviously are less productive but that doesn't mean that they can't contribute anything. That wouldn't be a problem in socialist society since the principle of "from each according to their ability, to each according to their needs" would apply. But it is a problem in capitalist society where everybody (apart from the owning class) is expected to fend for themself or rely on charity.
My sister used to work for the Department of Employment and part of her job was to ensure that companies fulfilled their requirement to employ a quota of registered disabled…She visited the Hibernian Football Club to check if they were employing any…the answer she got:" We employ eleven – we call them our first team. " Sorry to derail such a serious issue with frivolity…but i couldn't resist.