Language prescriptivism is an interesting form of elitism which allows people to feel themselves not only better, but smarter than others. Whether it's liberals making fun of Bush's pronunciation of nuclear, whites' mocking of black speech patterns, or simply bloggers attacking their opponents' grammar or spelling rather than their arguments, they are misguided about what language is and how it works.
If language is confusing, it's a problem. If language has "bad" style (for example if it's boring or cloying) is a subjective issue, but fair to note. Language is almost never, though, wrong.
"Damn, he dumb."
"Can everyone take out their books, please?"
"I don't feel good."
"Will all y'all shut the hell up?"
All of those sentences are perfectly understandable but often derided. What they generally reveal, though, is not stupidity, but the speaker's region and/or social group. There are undeniable advantages to certain styles in certain situations, for example speaking "standard" English at job interviews, "redneck" if you're Larry the Cable Guy, or "ebonics" if you're an inner-city black kid who doesn't want to be called an "oreo" by your peers.
Then there are the even snootier complaints made about the following kinds of sentences and phrases:
"To boldly go where no man has gone before."
"The train will be moving momentarily."
"Who did you go with?"
"Which begs the question of..."
Only the second and fourth can arguably be described as unclear, but they are so common, it's almost always snobbery rather than confusion that spurs complaints. The first and third are "wrong" only in the sense that some people have arbitrarily declared them as "wrong," in exactly the same way that one might argue that placing the fork on the right side of the plate is "wrong."
Sally Thompson at Language Log quotes an interesting comment about the nature of prescriptivists from linguist Lauren Squires, which I will reproduce in part:
Sociolinguistics is concerned with the question not only of how people speak, but of how they think about how they and others speak. You thus have people studying language attitudes, seeking to identify and understand what people think about linguistic variation: Why do Michiganders think they speak the most "correct" form of English in the United States? Why do people judge speakers with certain non-English-accented English as less socially desirable, less intelligent, or less agreeable than speakers without a discernible accent? How many Detroiters fail to recognize "Canadian" phonological features within their own speech community? (For excellent references on this topic, see Harold Schiffman's page of bibliographies on Language Attitudes.)
Then there's the language ideologies work, which goes beyond what people think about language to ask what social processes underlie the attitudes, often by appealing to political systems, historical influences, socioeconomic structure, and semiotic processes that turn language into a carrier of social meaning in various ways. Language ideologies are often defined as sets of ideas, attitudes, beliefs, and behaviors that influence how people use language (by imposing some sort of schema about what is "right," "appropriate," or whatever), and they also serve as speakers' means of rationalizing or otherwise explaining the language that they or someone else uses.
In the case of the United States, one can make a pretty good argument that our dominant language ideologies include ideas about there being one standard style that is considered "correct," that language can be something subject to judgments of "correctness" to begin with, and that nation-states are best off when their citizens speak one unified language. Studies on standardization, and particularly with regard to English, point out that in literate societies, ideas of "standard" become even more salient and powerful because of the tendency of print to "freeze" language or at least impose stratification on its use, elevating some formal or allegedly generic style above more colloquial or regional ones.
You can also argue that the written form serves as a trigger for linguistic awareness, on which there seems to be less research but which is of no less importance (if you ask me!). In order to make a usage gripe, you have to be aware of the linguistic feature you're griping about. You may be more aware because you were taught something about it, or you may notice it because it varies a lot among your acquaintances, or there may be something that makes it especially salient because of the kind of linguistic thing it is (phoneme, morpheme, word, spelling, etc.). You may also be more aware of it because it's been culturally packaged: invoking a term from Dennis Preston's work, a linguistic feature or language variety can become a folk linguistic artifact that circulates through the culture, picking up different social connotations along the way. Standard English is most certainly one of these, and so are "Ebonics," "Spanglish," "Southern drawl," and "Netspeak."
In public discourse (and educational settings), these are framed as distinct varieties to be either aspired to or avoided, having either high or low mainstream social prestige. We can pinpoint some contents of the artifacts, too, in media reports: about change in language as language decay, about linguistic "revolution" as socially harmful, about how no one sends thank-you notes any more, about how multilingualism is a threat to the health of English and Americans, about how emoticons are rampant in school essays, about how you'd better understand your teenagers' online lingo fast, before it's too late and they're pregnant or in rehab or, worse, cavorting with a sexual predator.
So, the gripers. You have people who believe that there's a correct way of speaking and writing, and who impose that belief on others. For them, what they are doing is fighting for the truth, tradition, and the Natural Order of Language. While lots of them may have some interest in language and its inner workings, for most, language is simply a material/symbolic system that gets roped into social Othering. Language is accessible, convenient, and flexible for use in doing so: it's always there, it's always changing, and it's always going to be socially differentiated. With linguistic variation, it seems that the grass is always greener on the other side, if you're talking about a usage associated with an appealing group of people (swoon those Aussies with their exotic diphthongs!), or it's greener on your side, if you're talking about a usage associated with a somehow undesirable group (shakes fist those Mexicans/teens/rednecks and their bad English!).
When you give gripers an outlet for their opinions, they're going to feel validated, and they're going to enjoy the feeling that their comments are helping to preserve the Natural Order. Maybe they see it as their duty, or maybe it's just a playful pastime. Either way, it's not (entirely) their fault, and it reflects issues beyond what people are taught about language. It's the reality of the social divisions we are constantly reproducing — every day, all the time, each of us. While I agree that it would be nice to get some teachable moments out of the gripes, I'm not certain that it would ultimately change anything until some deeper cultural issues were addressed.
Language Hat is another great blog that often touches on some of these issues. I also enjoy Mixing Memory.