"Productivity" is now effectively a privilege that can be revoked at somebody's whim: a boss or companies.
I've spent a significant amount of time around poor people. Those three supposedly magic words, "get a job," aren't easy or even always possible. If no one's hiring, what do you do to be "productive" in any sense (much less one that pays)? You can't just start growing food, or making things somehow. Other people own the land and means of production, that is they control the means of production or the ability to be productive....
That just gets more complex when you are physically disabled, never mind mentally disabled. Those both come in degrees and flavors. Fact of the matter is, we treat injured people like shit. Oftentimes, nobody cuts you a break when you even get temporarily injured. Quite the opposite, medical bankruptcies include not only a large portion of medical bills, but bills you couldn't pay because you were injured.... That's just on a relatively short term basis. Aflack? [collects $0.05]
People with long term disabilities, have a long term increase in expenses related to their greater health care needs. It could be continuing doctor's bills, or equipment. This is doubly true for people in wheelchairs, which if you are an able bodied individual, you simply are incapable of understanding. There are special machines and/or therapy to make sure you don't get blood clots in a wheel chair (which can travel through your blood vessels and kill you if you don't watch out). Same thing with bedsores from sitting. That doesn't even cover bathroom use supplies, even catheters, which add up. Fact of the matter concerning the physically disabled, is that it costs a small fortune to be physically disabled and that's if you're still able enough to work in any capacity. That doesn't even touch the fact that it is immensely more difficult to do EVERYTHING when you're in that position. We treat them like crap and it isn't right.
Even the people with lesser injuries are screwed. If you have a condition that makes it so you can't lift more than 50 lbs or even 25 over your head, then you're screwed. People won't hire/keep you on if you can't do that more often than not. My uncle tore up his shoulder at work and even though worker's comp is helping, it will never make him whole. Sometimes people who are physically disabled just don't have the skills to be doing a skilled labor position.
Then there's the mental disabilities, which again come in degrees and flavors. Some people can do some small form of labor, perhaps fast food, or bringing in grocery carts at the supermarket, but there are a fair number of people who can't, or barely can. Moreover, people tend to look down on them when they do those sorts of jobs or take advantage of them, which is a damn travesty.
Summation: Rewarding people for being productive is fine and good. Punishing people for things they often can't control, isn't. "Choice" is fundamental to the idea of rewards and punishments. If you can't chose what you're doing, then it makes no sense to reward or punish you, because without that choice there is no "encouragement."