First let me state the obvious—based on my own experience—that hordes of people are confused about certain basic grammar principles. For example, I so often see mistakes in choosing the pronoun to use with direct objects, especially when introduced by and with another person, as in "Joe talked about the book with Anna and [I/me]." Another one is the near 100% usage of "lay" instead of "lie" (and "laid" instead of "lay") nowadays, even in published sci-fi books that most certainly had professional editors proofread them.
Do you see these kinds of changes as predictors of the future? Will they become correct after enough people have used them long enough? Both of these problems drive me bonkers, and I fight my own little battle against them when possible.
I know that dictionaries are descriptive rather than prescriptive. They're technically history books. But grammar and style books seem less so, to me. Those seem as though they ought to be prescriptive in order to reduce the erosion of structured and meaningful language.
In this tension between "what people are doing" and "what people should be doing," are we doomed to forever bear these errors just because too many people don't know the proper way? Is it worth fighting against them? Do I capitulate to the people who are quick to accept any mass public usage as a fait accompli?
Update
I don't imagine for a second that my own writing is error free. The difference with me is that when I do learn I have something wrong in my mind, I immediately change once I clearly understand it.
I also am not imagining that language is static or ignorant that today's correctness is all too often yesterday's error. The whole point of my question here, then, is: is there value in slowing the change, and if so, how is that done and how effectively?
Another way to look at what I'm trying to ask is that in a way I am hoping to define the limits of pedantry. If being pedantic is slavish adherence to outdated rules in the face of actual and foregone changed reality, then when do we conclude that a change is a foregone conclusion?
Poking fun at my own errors to highlight supposed pedantry on my part is to miss everything I am trying to say.
Update 2
It may not be an easy question, but since language change actually does or does not happen, and every person acts with more or less intention in regards to language change, there must be an answer. What I wanted to explore is the value in efforts to teach the "proper way" vs. the opposite end of the spectrum where any new usage is not just accepted but welcome or even sought out. You know, I'm reminded of something: the conservative/liberal scale:
|------+------+------+------+------+------|
radical moderate radical
liberal conservative
The funny thing about those at the ends of the spectrum is that they both want things to change. The radical liberal wants language to change to something new quickly, just for the sake of newness or evolution or some other not-necessarily-realistic ideal. Similarly, the radical conservative wants things to change just as much, but back to the way it used to be, just for the sake of sameness or continuity or some other just-as-not-necessarily-realistic ideal.
I'm not particularly asking where we should be on this scale as that's purely subjective. I'm trying to ask about something purely practical and real-world: what is actually effective? Is language change inevitable, and how fast? Are efforts to reduce its rapid morphing either effective or worthwhile in any measure? All these things considered, what position with respect to language evolution is livable, practical, and sensible?
Feel free to edit my grammar. No comment necessary.
Update 3
Something that may be of interest to both my supporters and detractors: this 'Kinetic Typography' video by Stephen Fry. I enjoyed it. I don't disagree with him, but I am not sure I am wholehearted in this lack of disagreement.
Best Answer
We are most likely "doomed" in that these changes are more or less inevitable. But we are not "doomed" in the sense that the language is actually breaking or somehow falling apart. Languages have been around for thousands of years, evolving and changing; no language has ever evolved itself into a corner or created a construction that makes the language non-functional.
Many of the "correct" English words and constructions that we use today got their start as stupid-sounding "mistakes". Our case and gender systems have almost vanished completely, for example.
In fact, if I am not mistaken, a couple hundred years ago, "the only people who passed the test were Anna and I" would have been the pedantically correct version, and "Anna and me" would have been the sloppy "wrong" version; it used to be that the copula would have nominative case on both sides (e.g. "it is I", not "it is me"). Maybe that puts things into perspective a bit.
If you find certain things silly, there is nothing wrong with feeling that way and avoiding them — and not all variations become mainstream. But, it is pointless to try to make any significant effort to stop these changes. Mainly because it is inevitable, but also because you'd only be protecting a momentary instance of a thing that is constantly in flux.
(Edit: I should also add that I don't even necessarily agree with you in the case of lay and lie. Most people don't even know the correct paradigm for conjugating these verbs. I interpret the changes in popular usage to mean that these verbs are undergoing regularization; the old paradigm seems to be inherently confusing and I welcome the change: the language is fixing itself. I thought this might also be an interesting point of view to consider.)
Addendum based on the question's first edit: I recommend reading up on Standard Arabic to consider attempts to stop language change in its tracks. Because Muslims believe that the Arabic used in the Quran is holy, they have attempted to maintain this version of Arabic. This Standard Arabic is the only "official" Arabic, it is the only one they learn in schools, and it is the only one they write in. But, in day-to-day use, you can't stop language change. Instead, every region has evolved a distinct dialect (and these "dialects" really stretch the definition of that word to its breaking point). In many cases, they are not mutually intelligible (for example, Moroccan Arabic and Baghdad Arabic), and nobody in the Middle East actually speaks Standard Arabic as a first language. Most people have an imperfect command of it anyway except for the most highly educated. Most of the time, if speakers of different dialects want to communicate, they speak in a simplified hybrid of their own dialects and Standard Arabic (leaving off things like case marking that exists in SA). The Standard form has become different enough from their spoken language that they can't actually manage to follow the rules automatically.
This also means that if I want to learn useful Arabic, I have to learn Standard Arabic to read and for some TV programs, and I have to learn another language in order to actually communicate with the people around me. There is not much practical benefit to this system (but they aren't doing it for practical reasons).
If for some reason we decide to freeze English as it is now and make a concerted effort to maintain this form as it is, we will inevitably end up with the same messy diglossia situation that they experience now in the Middle East.
Addendum after second edit: I can't keep up with this moving target :)