Venice, my brother has cruised. He has no problems on a cruise ship.
It's not a tight enclosed space so if things get too noisey my mom or dad can take him back to the cabin. It would be interesting to see how the flight crew would handle my brother. But I agree with my parents decision not to go on an airplane with him. I have seen my brother in pure panic mode he could hurt someone with out meaning to. My brother is not violent at all. But if he sees a dog off leash, he will climb anything to get away from the dog including other people. Also if a baby is crying my brother will start shrieking and will be twice or three times louder then the baby that was crying. He just can't stand the noise. I'm sure either of those issues on a flight would be bad.