Yes, absent , there are several people here with relatives on the spectrum, and clapping can indeed be a problem. It is why some theatres run special performances of pantomimes etc - to cater for this need.
However, I have never believed in the principle of altering the normal activities of the vast majority to accommodate a small minority. Teaching life skills and coping strategies is of infinitely greater value - although not everyone in a similar position will agree with me.
DD actually proved to be far lower on the scale than anyone expected, when diagnosed in her twenties, and is affected by issues such as mass clapping. She attends large concerts! ...takes ear plugs, keeps them in her hand, and inserts whenever needed. leaves 5 minutes before the end whenever possible...or otherwise stays put until the crowds clear.
There are always workarounds to be found.
So, OP, whilst I think there should be a greater understanding of the incapacitating issues some people may suffer in certain situations, I agree with you that banning any normal healthy activity, enjoyed by the majority, is ridiculous.