There is a borderline between challenging yourself within reasonable boundaries and acting against your self-interest because you don't want to define yourself as a person with a disability. Passing is effectively denying the truth of who you are and the real possibilities in your life. We just happen to have this disability. I think a lot of people want to be assimilated into the mainstream and try to act the part of what they think people in the mainstream are like. Trying to pass as something you're not is always bad, unless you can carry it off so well and you have an emotional makeup that doesn't require honesty and authenticity.
Some people can be happy playing a role all their lives.
When people manage to pass, they're seen as successfully overcoming their disabilities by most nondisabled and some disabled people. If you can be free from having to prove yourself, your choices will not be tainted by this skewed motivation. If you are able to look at yourself honestly and with acceptance, you can see this motivation and not allow it to affect your choice. Passing doesn't have to be only about how you are viewed by the broader culture. People with disabilities are driven to substitute.