The movie illuminates how the concept of "disability" is a reflection of both family and societal values, which are then internalized by the individual and reacted to. On a societal level, it is clear that people tend to identify strongly with their disability, often feeling like their experience can only be understood by others who share it. This is likely in relation to how they function within society, and feel they are viewed by it. It is understandable that they react negatively to the idea of "normalization," through interventions, especially if they have battled against the idea that something is inherently "wrong" with them, and have learned to celebrate their disability as an identity rather than a defect.
I think the way that family values are internalized are harder to cope with. There is no other person out there who can fully relate to what you struggle with in regards to family expectations. Even the most caring parent's, such as the mother of the man with Down syndrome, worries that he has come to accept a "lazy" and "unchallenging" life, disappointed that his childhood celebrity didn't continue into adulthood. She struggled against his satisfaction with his lifestyle because she didn't view it as successful, despite his obvious achievements.