LetsFly<Snipped quote by The Nexerus>
But that line between what you view as intelligibility and actual evolution in dialect and slang in pockets of culture is basically impossible to define, attempting to organize any set of rules for language based on intelligibility and avoiding ambiguity should be exactly that. Governing beyond understanding on a casual level is simply emulating some archaic linguistic history for the sake of those setting the rules. In the context it's fairly easy to understand what "..Post if Your Depressed" means. It isn't laziness, it's people realizing conflating the two words is convenient and the next step of evolution for the word-- you can understand what is being said based on the context of the sentence.
In this case, yes, it was clear what meaning was intended - but that would not be so in every occurrence of a your/you're mix-up. You cannot, therefore, simply conflate the two words at all times without at some point creating unnecessary and excessive ambiguity.
Nor can you say that the words should just be conflated sometimes; that one should only bother to differentiate between the two, i.e. stick rigorously to the rules of the language, when one believes ambiguity may be caused. By doing so you would simply introduce yet another layer of confusion, adding into the equation the questions "are they bothering to differentiate or not, here?" for the reader and "should I bother to differentiate?" for the writer.
One can only conclude, then, that the two words can never just be conflated. They must be kept separate and used appropriately.
The rules of language exist as a method of standardisation, to ensure all people who speak the language can mutually understand one another. The only rules that should exist are those that aid in this endeavour - I agree with you on that account. But this is the thing: rules must be rules, not vague guidelines to be followed at whim, or else there is no point in having them. If rules are treated as guidelines, to be ignored or dismissed at random according to the fancy of either reader or writer in the moment, they simply end up self-defeating and neutered in their effectiveness. They must be abided by at all times in order to avoid this; in order for language to fulfill its one and only purpose, which is to communicate. Ambiguity is a language's greatest foe.
Now, admittedly this all seems very much like an "on principle" sort of thing, I know. In reality it's okay to bend the rules or make mistakes, and people will often still understand you. But upholding those principles is still vitally important - because if you don't then, as you said, over time things will evolve - they will just get messier and messier until your language is very inefficient and difficult to communicate in. Which is not what you want.
