All jokes have a victim. To not take the piss out of one section of humanity for any reason i feel is condescending. Do people with disabilities not have the ability to laugh at themselves? The ones i have spent any time with do. In fact to treat them as victims is about the worse thing you can do, a lot also like to take the piss too.
I think it was called, I am spazicus(i think) on channel four, where a group of cerebral palsy sufferers get a passer by to do a police line up and act like them is funny, because the lads in the line up are cracking up.
Laughing at the bad hands you have been dealt is a coping strategy. The outrage is probably from some idiot not affected by disability and feels it should be degrading.
Apologies if you are affected by disability and i am open to be educated if i have overstepped your mark, it is only through my experience i have come to this conclusion.