I don't see why the actor has to have a particular disability just to portray a character with a disability. It's called acting for a reason. These people are playing pretend and portraying the role that was given to them. If we stuck an autistic kid in a role just because his/her role has autism, that's not really acting, it's exploiting someone's disability for personal gain.
For instance, Gary Sinise from Forrest Gump. We didn't go out looking for a guy with no legs, just because his character had no legs.
Most actors/actresses who have to play a person with a disability or impairment, usually study people who deal with it to give their performances an authenticity. If people want to believe that this is empowering or insulting to people with that disability, it's their choice. This is the entertainment industry after all, their job is to entertain us 1st and preach its message 2nd.
Also lets not forget that there are entertainers out in the industry who have disabilities and more often than not are portraying normal people...most likely because I doubt they want a "pity party".
Howie Mandel is color blind, has OCD, and is severely afraid of germs, which is why he doesn't shake hands. Instead he bumps fists with people on his game show.
Michael J. Fox has Parkinson's Disease and is known for hiding his hands from the camera so people don't see the twitching.
Even Tom Cruise himself is dsylexic. I'm sure that must have been difficult since a large portion of his job involves reading scripts.
People can think what they want about disabilities in the media, but even big name stars have issues of their own to deal with.
