Expansion of the term as I described is more like expanding the term "bread" to include more than Wonder Bread. The kind of marginalizing and persecution you describe already has many words that refer to it: discrimination, and the more specific sexism, racism, anti-Semitism, gay-bashing, and so forth. "Political correctness", as I have seen it in actual usage, refers mainly to speech, with a focus on perceived offense vs. actual content, which I why I presented the examples I did.
What you have seen in "actual usage" is people misunderstanding the term. They are the exact same people you have a problem with, the ones who misinterpret a variety of cues like the use of politically correct language, or anti-discrimination laws, or efforts by companies and politicians to not alienate potential customers or voters in any way, to mean that they have a right to never be offended. They are, of course, incorrect. Instead of pointing out to them that they are incorrect, you instead concede that their mis-interpreted observations are correct. From there the argument devolves into "It's ok to offend people!" - "It's not ok to offend people!". This will never be a productive argument because it is sometimes ok and sometimes not ok and it mainly depends on how and why you are offending them and why they feel offended, and there are some gray areas in there. It's the particulars of a situation that matter. Otherwise you'll just be throwing anecdotal evidence at each other all day and never come any closer to understanding or agreement or change of any sort.
The collective decision you refer to is hardly universal. Substantive discrimination persists in many forms and settings, and the consensus on proper terminology is limited, tenuous, and often localized at best. Political correctness does not cover every form of offense; it focuses on the offense taken by (or often on behalf of) people in marginalized groups due to matters of speech and reference. This interpretation of the definition may be unfamiliar to you, but prevails in the three US regions where I have lived. This just goes to show how little consensus there really is on definitions, however much most of us may agree on the need to promote equality.
Wait, so apparently there IS a specific, agreed upon, definition of political correctness (and you are apparently aware of it). Even more interestingly, you agree with the need to promote equality, which is the point of the exercise.
No, it's not universal (otherwise there'd be no racists, sexists, homophobes, etc). It's pretty close, however: you will face a lot more and worse social pushback for using racist slurs than you would for calling any given person an asshole. It goes with the promotion of equality thing.
Also, having specific terms for people who are chauvinist against a specific group is not the same as having a blanket term for instances of such chauvinism.
In "the USA I live in" as you put it, many people do consider "African-American" as the only acceptable term, though actual black folks are rarely put out by being called "black". When the topic comes up, those espousing "African-American" are often criticized as putting political correctness over effecting substantive change: IOW, arguing over superficialities instead of making a real difference.
Yeah, you mean the same folks who misuse "political correctness" to insist that no one should ever offend anyone are the ones getting their panties in a twist about using a term to refer to a group that the members of that group themselves don't mind? Imagine that. Maybe someone should spell things out to them. They'll be the same ones throwing around racial slurs if you persuade them political correctness is a bad thing, since they clearly can't tell the difference between discrimination/persecution and hurting someone's feelings.
The second of my examples is not politically incorrect, it is factually incorrect. The first contains the term "negro", which now is considered politically incorrect. These examples highlight the distinction I am trying to make, between superficiality and substance, feeling and fact.
Things can be incorrect in many ways. The second statement's factual correctness is beside the point -- of course it's factually incorrect. It also invokes a racist stereotype, which makes it politically incorrect. If you said that all black people had wings, well, that would be factually incorrect and politically neutral. You are trying to create a distinction where none exists. Being politically correct does not require ignoring facts or saying outright falsehoods. Saying that blacks make up only 12% of the population of the US but 37% of the prison population is factually correct and therefore also politically neutral, whether or not it seems to imply an extra-high prevalence of criminality among black people.
It is simply viewing people as individuals, and recognizing that words have no meaning other than what we infuse them with. You wouldn't want me to make other blanket assumptions about blacks, for instance: that they are less intelligent, or like fried chicken, or are good at basketball; even though at least some will have these qualities (just like whites).
It doesn't quite work that way. Treating people as individuals IS the intended point of political correctness. NO, words have meaning outside of what you PERSONALLY infuse them with -- there is a consensus of word use by populations, it's called language. That's how you know "water" means that wet stuff coming out of your tap. Political correctness is intended to alter word use and the use of stereotypes, such as the ones you have just trotted out, in order to alter the cultural landscape at large to the point where no one thinks these things. The idea is that when everybody keeps saying these things they keep being reinforced. So they need to stop being repeated like a broken record. That is the ultimate purpose of political correctness (sparing some people's feelings in certain ways is only a slice of the pie).
Yet you want me to assume they all prefer to be referred to in the same way.
They do. Or, rather, they don't want you to call them "Negroes" or "Niggers" or "Coloreds". Furthermore, they want you to stop trotting out that fried chicken crap. How do I know this? Well, I've discussed it with some black people personally. I've heard and read many other black people state the same thing. I can also imagine how sick each and every one of them is of every dude thinking he is being witty and trotting that shit out. Since they are a persecuted minority (and I am not), I think it's fair that I assume that the people telling me these things know of what it's like to belong to that minority (while I don't) and tell me how not to perpetuate the problems they deal with every day.
If every "Robert" I ever met wanted to be called "Bob", I might reasonably expect the same of the next Robert I meet. If he wants to be called "Robert", however, I will go along as a matter of personal courtesy. That's the only right or wrong here: whether you respect an individual's preferences, or not. You can assume you know this based on trends, or other people you know, but it is exactly that: an assumption.
Here's the problem with your example: being called "Robert" is a completely neutral fact and has never been cause for persecution. So, no, you can't make any assumptions about any given Robert's preferences for the form of their diminutive name. I'm willing to bet that if every single Robert you ran into was mistreated for being called "Robert", and if, furthermore, that mistreatment involved referring to "Roberts" as "Bobs", things would be very different. And since this persecution would uniformly apply to any Robert, it would also change how every Robert feels about being called Bob. So no, not all assumptions are equal: some are much more likely to be true.