It depends on the state, and the laws there with in.
It also depends on how intelligent and aware the mentally retarded person is.
I should post it, but in Life News was a story about two Down Syndrome people who got married. Now those two would be allowed to have sex. That would be an example of an exception.
However some persons with Downs don’t understand what sex is because their IQ is so low. To try to do it with them would be the same as molesting a child.
Same as I just said, good.
We had a dear friend who lived with his parents. He was intellectually impaired and in his late 30s. He had a “girlfriend” with Down syndrome in NoCal who would come down and stay with them. The both sets of parents made it safe for them to be alone together.