So I actually went and read the ADA (at least the relevant parts, I ignored things like employment or public transportation) and I found a couple interesting things. First off, I noticed that there is a term "qualified individual with a disability". This term changes from situation to situation, but essentially it states that the individual must be capable of meeting the most basic requirements to participate in programs or activities in order to make reasonable accommodations to make that possible. If the person has been traumatized and can't be exposed to sexual content, then it would seem that they don't fit the criteria for being a qualified individual with a disability. If they can't learn the material because the material itself is a barrier, then they are not eligible for accommodation. If they aren't learning because the teacher is doing something that prevents them from learning, that needs to change. However, if the class is about sex in films, you could reasonably assume that to learn about that you need to watch films and the sex that takes place. If you're incapable of doing that, you need to check your reality.
The ADA also defines discrimination in regards to public services:
Subject to the provisions of this subchapter, no qualified individual with a disability shall, by reason of such disability, be excluded from participation in or be denied the benefits of services, programs, or activities of a public entity, or be subjected to discrimination by any such entity.
No one is being excluded from participating in the class or denied the benefits of the program, they simply can't attain them because the course itself is a barrier for them. This would be like me trying to join a track team if I was a paraplegic. If you're incapable of participating in the activity at its core, then you shouldn't be trying to participate. You should find something more suited to your abilities.
IANAL but my final opinion is that there needs to be laws written to address this, because the ADA doesn't. The ADA was written almost entirely with physically handicapped people in mind, most of the act is about how people need to change either physical infrastructure or their methods of conveying information, not actually changing the core of an activity to fit someone's comforts.
Feel free to read more of the ADA here http://www.ada.gov/pubs/adastatute08.htm and if you find something to counter me with, I welcome that since I'm no expert and can always learn something new.