So are you saying that you don't believe that the introversion/extroversion spectrum is a real thing that can accurately describe people, or that you just don't like the way people are using those labels as slanders or badges of honor?
No, the difference has been tested to some extent. It's extrapolation that's the problem. I see people talking about introvert vs extrovert ALL THE TIME on Facebook and every tenth blog article. Since the last article linked was a bit cruel and way too facetious, here's the problem with it put more eloquently and less sarcastically:
http://thesocietypages.org/cyborgology/2013/08/29/the-introvert-fetish/
It's totally understandable anyone could be jaded by a large society constantly pushing for "outgoing" and "charismatic" traits, and how anyone could be jaded by a flurry of meme images mocking them for having plenty of friends, but reversed stupidity is not intelligence.
Yeah, I mostly agree with everything in the introvert fetish article. Never dug as deeply into the root origin and meaning of the fetish, but I've definitely recognized it and been very annoyed by it, as I described before. It's all just a bunch of immaturity, though, and it comes from all sides, like you said.
Definitely doesn't mean that the subject isn't worthy of awareness, though.
Introversion vs extroversion is really not meant to represent anything more than stimulation threshold. The more introverted you are, the lower your threshold, and the easier it is for you to be over-stimulated. That's really all it is. This is an easily observable thing that people tend to be fairly consistent about, and can only fail to describe a person as much as one can fail to be described as short or tall. I think the same can be said for the other three spectrums on Myers-Briggs as well.
They're absolutely not meant to paint a complete picture of a person. Just like not all short people are the same, not all introverts are deep and intelligent. The people who try to frame it as such do not know what the hell they're talking about.
But there are clear differences in the way someone's stimulation threshold can effect how one experiences life and interacts with society, just as there are in the way a really short person experiences the world vs a really tall person. Being formally aware of that subject is important for making society more inclusive. For example, public schools might realize that they're mainly designed around the needs of extroverted children, and sort of force introverts to just tough it out. But that's never going to happen unless the whole thing gets taken seriously as a little bit more than pseudoscience. You don't need hard science to recognize that a certain terminology can be useful for describing human features, and that simply having the proper language in place can go a long way towards building useful understanding.