The intellectually disabled and bodily autonomy

In your brother’s situation, it seems like there’s a lot of supervision available, and they’re used to that. So ISTM that requiring supervision for their dates would be reasonable, and even if they were allowed to be alone together for brief periods, which would be nicer for them (I couldn’t work out if being alone was something that could happen), they could be very limited, with people always walking in and out. So it seems safe.

The main issue, really, would be, what if they broke up? At school, that can be an issue, but they don’t usually live together. It would be worth talking with the staff about how they’d handle it.

In some respects, it would amount to telling adults that they can never have sex ever. But they are also not allowed to drive motor vehicles - they are not being treated like adults, because the repercussions of those adult choices impact others.

Oh and I thoroughly loathed the movie 50 First Dates too, and truly don’t understand how anyone can watch it all the way through and still like it.

The issue I have with this is that they do not have an innate biological desire to drive a motor vehicle. I share your concern, and I might get flamed for saying this, but I don’t necessarily think that sterilization is a bad option to consider in some circumstances. That would at least allow them to satisfy their sexual desires without causing harm.

Sterilisation is extreme. People have been obliged to get IUDs - even Britney Spears was forced to get one. That might help in some situations, especially if the person was - in some respects at least - able to understand what an IUD is. But in this one it’d be, well, contentious at least, to tacitly allow someone with a mental age of five to have sex.

Bill of Rights for People with Developmental Disabilities

  1. You have the right to be treated with respect.
  2. You have the right to a clean, safe place to live.
  3. And you have the right to a place to be alone.
  4. You have the right to have food that is good for you.
  5. You have the right to go to a church, synagogue or mosque if you want to.
  6. And you have the right not to go to one if you don’t want to.
  7. You have the right to go to a doctor or dentist when you need to.
  8. You have the right to get other health care services, like speech therapy or physical therapy if you want to.
  9. And you have the right to get mental health services if you want to talk about your feelings.
  10. You have the right to get these services in a way that makes you feel comfortable.
  11. You have the right to be alone sometimes. And you have the right to keep some things private if you want to.
  12. You have the right to talk to other people.
  13. You have the right to have your own things. And you have the right to use your things.
  14. You have the right to have men and women as friends.
  15. You have the right to do things that help you reach your goals.
  16. You have the right to work and make money.
  17. You have the right to be treated fairly.
  18. You have the right to live without bullying or abuse.
  19. You have the right to do things you enjoy.
  20. You have the right to help make decisions that affect your life.
  21. You have the right to choose someone to help you make decisions.
  22. You have the right to earn money and pay your bills. You have the right to save your money and to spend your money. And you have the right to choose someone to help you with your money.
  23. You have the right to say who can see information about you and your disability.
  24. You have the right to ask for changes when you don’t like something. And you have the right to ask for changes without being afraid of getting into trouble.
  25. You have the right to refuse to take medicine you don’t think you need. You have the right to be in control of your own body.
  26. You have the right not be held down if you are not hurting yourself or someone else.
  27. You have the right to vote and to learn about laws.
  28. You have the right to decide if you want to take part in a study or an experiment if someone asks you to. You have the right to say no to taking part in a study or experiment.

#11, #20 and #25 all seem to be relevant here.
Since the staff who care for the clients are not going to restrict client sexual activity unless they are under a court order (anything less is generally held to be a rights violation), it would be ridiculous to sue them. People with ID have the right to have sex, even if they have been judged incompetent by a court. They have the right to do other things as well that are not the best choices, like not clean their houses, or eat junk food exclusively, or refuse to brush their teeth. Like the rest of us, when they do things that they shouldn’t do, they have natural consequences.
As long as Stephen and Becky each consent, they can have sex. They aren’t likely to be that interested as they are developmentally younger, but consumers who function more at a teenage level of development probably would should they find a consenting partner.
They aren’t children.