Hammer, there are a good number of unknown 'bodybuilders' or 'fitness guys and gals' trying to get decent movie roles in Hollywood and they are definitely not 'retarded'. Most are involved in behind the scenes stunt-work because for the most part if you have hopes and plans of becoming a principal actor, you don't want to be 'classified' as a stunt performer.
And I believe that an unknown actor with a bit of acting experience who resembles a super-hero as the artist originally intended would be great for the production as long as he didn't have to recite Shakespeare or battle Al Pacino in the opening sequence.
If you only know 'retarded' bodybuilders, it might be a good idea to change the crowd you hang around with or simply view them from a different perspective.
I have only met two real bodybuilders whom I thought acted somewhat retarded. One such individual actually wore a Superman costume under his heavy wool suit while going to High School, but many years later I found out how smart "Supe" really was when it came to helping friends in need.
And the other kid who lifted heavy things since he was 12 definitely did have mental deficiencies but has received numerous citations for helping others who are even less fortunate than he himself.
Both these 'Super - Heros' taught me to never judge a book by its' cover because inside that "book' is one heck of a big heart in addition to all that muscle!