I agree that presenting yourself intelligently is important, but it's not just about appearances for me. I don't necessarily mind abbreviations, and many things that would be considered "obscene" don't bother me, so long as the person put at least a modicum of thought into what they say.
And as to the point of view that says it's acceptable so long as it can be deciphered... how long will it take before you *can't* decipher it? The point of having rules of grammar is the same as the reason you have rules of the road. There may be specific reasons for some of them (use "an" instead "a" before a vowel-like sound, because it's simply a lot easier to say and sounds more pleasant), but the biggest reason is just to have a consistent set of rules, so we can all read anything written by anyone. You cast those aside, and in the next couple years or so we'll be fine. It's 10 years from now when every single person continues to write whatever he/she wants that you'll start looking at sentences and actually having to ask what is meant, because you simply cannot understand what is being written. Even *with* consistently applied rules, the natural evolution of language ensures this happens to a degree anyways (look at how many people, sadly, struggle with Shakespeare); why accelerate the process?
Personally I dislike the deciphering option. Yes anyone can make a grammar or spelling mistake, especially if a language is not one's own. Just using any slang and internet lingo is also allowed but it makes reading and understanding the message a lot harder than any well-written comment.
Then there is my observation that _most_ bad-grammar comments have relatively shallow content. These things combined usually make me stop reading after a few words. If a person doesn't think his message is worth stating clearly then it is probably not worth the trouble of deciphering it.
Simply put, first impressions are important and grammar, spelling and good use of e.g. commas are part of that.
It matters to some, but obviously not others. What we see is the collision of two attitudes: If you're going to write something, do it right, versus "Just as long as it can be deciphered by the reader." I see no reason to write terribly, and I dislike when people don't make the effort. But that's my view, and I guess that of GalaxySpinner as well. In the end, language is what people make of it, so we each do our part to make it what we want it to be. And whenever people disagree, there is potential for argument. But argument isn't a bad thing, only hatred and illwill.