Rant: "Overqualified"

I am confused about a way of thinking that has recently come to my attention. The core of this belief is "over-qualification," as in "I am overqualified to do that job".
What does this mean?
The example I will give to you is an engineering major who has recently graduated from university. Upon finding that there are no engineering jobs available in the area, the engineer searches major job sites for other available positions. The only place that's hiring is a high school looking for a janitor. The engineer thinks, "whoa, no way. I am totally overqualified to be a janitor!"

Stop. What?

How is an engineer overqualified to be a janitor?

Think about it. That is ridiculous. They have zero parallel training, wherein the engineer would have superior custodial abilities to the janitor, thus making him overqualified to scrub toilets and mop floors.
If anything, the engineer is under-qualified to be a janitor because he has pretty much no prior experience in the things a janitor does, aside from skimming the top layer of grime off of his college apartment every six months. It is ludicrous to think that just because he is an engineer that his experiences somehow elevate him above those of a janitor. Likewise, a person trained as a janitor would not presume to think that he is overqualified to be an engineer (although sometimes that janitor is an engineer). Is it not strange that it seems so obvious to us that a janitor would not think he could simply do the job of an engineer but not the other way around? Can't both the janitor and the engineer learn to do each other's jobs equally well?

What I'm getting at is that nobody's job is inherently "better" than someone else's, nor is anybody better than someone else based solely on their life experiences or training. We all need each other. We need the engineers and the janitors, the mechanics and the lawyers (yes, we need the lawyers). If the job were unnecessary, it wouldn't exist.
I think my point is that a lawyer shouldn't scoff at the guy fixing his BMW. He needs that guy. And an engineer shouldn't look down on a janitor. Our lives would be filthy without those guys.
We have our jobs, and hopefully we do them well. Every job deserves credit for the individual difficulties that job presents to those who do it. We should not minimalize jobs that may not require a higher education to do. They are just as necessary, just as noble.

So no, you are not overqualified for the job. You just haven't learned how to appreciate it yet.