I would like to share with you, I just registered on the page and your story was the first one I read and it definitely struck a cord with me. I am also in my late 30's (39) and actually am technically disabled as well. I have seizures, so not as obvious as a wheelchair - but still.
Another thing, ironically, I am a performer. I was in a small production here in the villages a few months ago "Montana: No Fracking Way!" just as a chorus member, and just got cast in a new production "Man of La Mancha". Anyone who comes to see a performer, that performer appreciates, even needs in their heart, and to see a reaction from the audience is their "bread, butter, and the whole sandwich". The performer gets more excited and into the show when the audience reacts well that night - laughing at the right times, clapping at the right times. There have been lots of times when you compare one night to the other and say this one is a "bad/dry audience". Every performer who ever saw your son clapping and getting into the performance would have gone up to this guy and asked him to leave!! Demanded it!! It would be one less in the audience, but if their is someone ruining the event for others, its worth it!
I do hope you did not have to sit far away from your son. Sharing the experience together is half the fun!! Talking about how one guy was funny, one girl is wearing a weird dress, things that make you laugh!
Big hugs! From every performer you have seen and will see!!