Makes sense to me. 

I'm personally with a mild disability, colour-blindness. However it makes my vision extremely sensitive to movement and low light situations. So you do have a point. 

Also, keep in mind that technology might make those disabilities obsolete, creating better quality of live for people.  Especially for those suffering from chronic pain and debilitating degenerative diseasses.  

I want to believe in having the blind and the deaf in space but I don't think it will happen since there needs to be communication in something so dangerous. 

The elderly may not experience as much pain but the pain they feel when returning to Earth would be too much for them.

Most examples have something going against them as well. I'd love to hear other's thoughts on this as well though!