Your opinion is completely unsupported by evidence. Do you truly believe someone with Downs Syndrome or a severe traumatic brain injury has the capacity to be a theoretical physicist?
The belief that everyone is capable of great things might be comforting, but it's ultimately very cruel. Many people will try their very hardest and get the best available support, but still struggle with the most basic tasks of life and work. Pretending otherwise just absolves us of responsibility. It's a get-out-of-jail-free card when we see people suffering.
We need a society that provides a good life for everyone, regardless of their ability to contribute. It's great if truckers can retrain to be software developers or psychotherapists, but we shouldn't be planning our society based on that assumption. Some people are very unlikely to develop advanced professional skills, but that's fine. They're still human beings and they're still entitled to a dignified and fulfilling life.
There are all sorts of "intelligence" that I just don't have. I don't get social cues. They just don't register for me. There is a "social intelligence" that I don't have. But I have seen people who clearly do.
Likewise, there are things that I find to be quite natural for me, and other people look at me like I'm crazy and they don't comprehend how I can do those things.
Whether you call it "intelligence" or some other word, I think the result is the same.
The Johnson O'Connor Research Foundation (http://jocrf.org/aptitudes) uses the term "aptitudes":
> Aptitudes are natural talents, special abilities for doing, or learning to do, certain kinds of things easily and quickly. They have little to do with knowledge or culture, or education, or even interests. They have to do with heredity. Musical talent and artistic talent are examples of such aptitudes.
> Some people can paint beautifully but cannot carry a tune. Others are good at talking to people but slow at paperwork. Still others can easily repair a car but find writing difficult.
Is that a better term than "intelligence" for what you had in mind?
Ironically, this directly contradicts your point of view, since your maximum physical potential is strongly determined by your genes. Only very few people have the potential to be a Usain Bolt or a Michael Phelps.
> Every single human being has the potential to be an Einstein, so to speak, in my opinion [...]
Well, it seems that your opinion is wrong, then.
In any case, since most people have not had the fortune of having the good experiences that most of us here have, I think it is merely a common service to our fellow man and woman to treat them equally no matter what and provide equal opportunities for employment -- and that includes whatever the en-vogue measure of intelligence is out there today.
* to be fair to me: I formed my opinion over years long soul searching and embellishment in countless self-help and pop-sci books on self-improvement, finally forming opinions around sound science and not junk science. But I am also a human after all, and admit my understanding of the current literature can be flawed.