The issue with the prescriptive vs. descriptive conflict is that "but everyone spells/uses it that way" doesn't make it right. Linguistic shifts are normal and natural, but misuse through ignorance is not something that should be encouraged, especially in an era where we've finally managed to nail down consistent standards. One of the major reasons for older writings being more of a strain to read casually is because people spelled, punctuated, capitalized, etc. however they pleased, according to their own standards. This isn't bad by default, and in fact can be used to great effect, but there is a difference between (say) Dickinson's use of em-dashes and someone who doesn't use question marks for interrogative sentences because they don't know or care that one is supposed to.
When standards are ignored either because people don't understand them or are too lazy to adhere to them, it causes problems with comprehension--see the difficulties in communication between people from different regions who speak the "same" language, and then imagine that translated into textual communication as well, via dialectic spelling, punctuation, etc. Long-short = You need to understand the rules to break them.
That seems rather conceited.
The "grammar nazi" thing is fairly recent in the history of communication (in that they have a set of "strict rules" to beat people senseless with), while the "complain about the youth misusing words and phases" thing is at least as old as ancient greece.
The grammar nazi relies on the modern contrivance of standardisation; language has historically not given a squat about that.
I see this quite frequently in fact, where new technology or new social settings create neologisms and portmantaeus made from malapropisms (ahem.. like the infamous "malamantaeu", but also more appropriately with things like "lol". The grammar nazi comes unglued seeing these words used, shrieking to the stars above that "Those aren't even real words!". Heaven forbid that the words use purposeful misspellings or misconjugations for impact.) Are used, and the grammar nazies come out in force. At what point does the meme become a fixture of language? After all, things like "hit the bull's eye" and "struck the jackpot" are little more than aphorisms taken out of context and time, being applied to things often wholly unrelated to the original intent. The differences between such fixtures and memes that have lost their original meaning is pure academia. Functionally, they basically the same thing. At what point does a meme gain admission, in the face of the grammar nazi? When the old nazis finally die of old age perhaps?
The grammar nazi wants to assert, (for the sake of standards, of course!) That these kinds of uses are simply wrong, and can never be in the dictionary-- they curiously never seem to account for the large number of such features that are present in the language and in the dictionary already however.
The adoption and use of neologisms, and the POPULAR USE of spelling is what HAS historically driven the evolution of written language. See for instance, "color", -v- "colour". The brittish grammar nazi will go purple trying to argue with the american grammar nazi about which is correct.
"We finally have standards!" Is asserting that you can freeze the river.
It doesn't hold.