There is also the matter of physical disability. I believe that is included in Affirmative Action, but if not, it certainly is in the Americans with Disabilities Act.
I don't think that I, personally, have been denied a job because of my physical disability (polio at age two, walked with forearm crutches all my life; now, due to wear and tear on the shoulders from walking with crutches all that time, I use a wheelchair), because I never applied for a job that I couldn't do or at least learn quickly, and at interviews I tended to come on strong. I interview the interviewer, because I want to make sure I actually want that particular job. I've found that approach gives a whole new tone to a job interview.
A few years back, shortly after I started using a wheelchair, I applied for a job as a "word processor" (this was when knowing how to operated WordStar, Multi-Mate, or MS Word was a specialized skill that not too many people had acquired yet), and there, I got my first hint of the kind of thing that someone in a wheelchair can run into from time to time.
Since the place where the interview was held (not where I would actually be working) was down a long maze of hallways in one of the more sprawling buildings on the University of Washington campus, my wife accompanied me, pushing my chair when my arms pooped out. She came into the office with me and was going to wait in the reception area while the interview took place. The interviewer came out, and after introductions were made, she started out by directing her questions to Barbara, referring to me in the third person, as if I were some inanimate, uncomprehending object, not an intelligent and alert human being sitting right there in front of her. Barbara said rather stiffly, "I believe my husband is perfectly capable of speaking for himself."
The interviewer turned her attention to me, but began speaking loudly and slowly. It took her several minutes of conversation to catch on to the fact that I was not sitting there rolling my eyes and drooling, but was indeed intelligent, alert, and getting a bit pissed off. As is my wont, I turned the interview back on her, and started asking her questions. I learned that, among other things, the material I would be dealing with was tediously dull, and the pay was minuscule. So I thanked her for her time and said, "No, I don't think so, thank you." I wasn't just being snotty, I really didn't want to do the kind of work she outlined. I could do better than that, And indeed, I got a much more interesting, better paying job a few days later.
Many people seem to be under the impression that a physical disability is automatically accompanied by a reduction in mental capacity. If you can get by that hurdle, many employers are reluctant to hire someone with a physical disability because they are afraid they'll be required to make expensive modifications to the workplace to accommodate the person, when more likely than not, the only special consideration they need is for the rest rooms to be wheelchair accessible—which is required by law anyway.
But to fill in the picture, I know a few developmentally delay people (used to be referred to as "retarded") who, if given a job within their capabilities, make diligent, hard-working employees.
Affirmative Action and/or the Americans with Disabilities Act legally require that employers give due consideration to people who, for one reason or another, have all too frequently been shunted off to the side and forced to live on welfare instead of offering them a opportunity to earn a decent living by contributing to the community.
Said employers often have to be dragged kicking and screaming into acting in their own best interest.