My attitude with teaching disabled riders was that if they got themselves to the arena without help, on sticks, in a wheelchair or crawling, then there was no reason why they could not ride a horse as an able bodied person.
All to often disabilities are used as an excuse by the instructor not to push the riders to achieving what they are capable of therefore they are just giving the riders 'pony rides'.
Many years ago, way before it was accepted that disabilities meant you could ride, a young girl, paralysed from the waist down by Polio, was brought by her grandparents to look at the horses. Both her legs were in callipers she was allowed to pat the ponies with her grandfather holding her which was silly to my mind as it was an effort for him to carry her. (She was about 8 years old)
One day I lifted her onto a pony bareback and led he around. The joy on her face was something I will never forget. She started to ride, she was led out from another horse and learned as an able bodied person. Before long she was spending the day working at the stables, the kids were great with her accepting there were things she couldn't do but making sure she did her fair share.
Jo was a natural rider, on a pony she looked no different to others. She was certainly not one for saying "I can't" and was soon competing alongside others of her age.
At the age of 11 she was show jumping. She was competing cross country, she was fox hunting.
At a major national show the girl who competed on a very good 13.2 pony was taken ill so Jo took over the ride. The class was for 14.2 and under, ponies and as a junior open class they started at 3'9" first round. Jo went clear in two rounds and in the jump off, as they came into the wall I could not see either of them!
Inexperience meant they came 3rd as Jo did not cut the corners as much as the pony was capable of.
So, having seen what a disabled person was capable of I will not accept that they have to be led around but will push so they have total independence when riding.
Sure thing that some will not be able to achieve as much as others but generally speaking, they can achieve a lot more than most will settle for.
It takes a special horse/pony to help with these riders but that does not mean they should be 'dead' they should be responsive to all sorts of aids and should be trusted to know what is wanted of them.
There are always going to be riders who can do nothing more than sit on a horse with a person on either side to aid their balance but, even they can learn and improve.
As for cons, I cannot see any that are anything different from an able bodied person. Yes, riding is a risk but that is the same for both sets of people.