My opinion: a rising tide lifts all boats. This NPR article explained how the ADA Act has helped more than just people we traditionally envision as “disabled.”
The wider use of elevators, ramps, and other wheelchair accessibility issues has made life easier for the elderly who may have mobility issues or trouble negotiating stairs. Young families with little children (and strollers, and bags, and toys, and sometimes even the family dog) appreciate easier access to buildings. I doubt that anyone but the most hardened cynic would claim that having a wider range of people have access to public areas is a detriment.
ADA accessible transit has also improved transit for the elderly and the very young. Public transit is an issue close to my heart. I commuted into downtown Seattle for many years, and even the most hardened cynic of the previous example would have a hard time denying that Seattle traffic is a mess, and getting people off the roads and into buses is one solution.
Let us also not forget that there are invisible illnesses – people with wasting diseases, chronic fatigue issues, or even HIV, cancer, or MS fall into the ADA's category of a disability. Just because we cannot see that someone is sick doesn’t mean that making their lives a tiny bit easier is not a force for good.
As a final note – 1 out of 5 Americans are considered “disabled.” A disability can be a wheelchair or chronic disease, or it can be deafness or visual impairment. Arthritis is the most common disability – which makes grasping non-ADA compliant knobs difficult, and necessitates the use of levers on so many openings.
This is general politeness, in my book. You wouldn’t ask a person in a wheelchair what happened to them, and I feel people who look fine on the outside deserve the same kind of respect.