I spend too much time reading online posts and have lots of experience playing online games so I have plenty of experience with badly written thoughts. I generally don't bother playing Captain Grammar because it never seemed to accomplish much but I certainly preferred the company and commentary of people who communicated using something resembling normal english. Boingboing just posted a fantastic piece on the topic talking about literacy being a privilege and it certainly shed some light on the topic for me.
A lot of people due to disability, life circumstances, or place of origin really don't have the capacity to write english in a way that I would deem 'correct'. That doesn't mean that what they want to communicate is less valuable or that there is anything wrong with them. Pedantically correcting their grammar or spelling is a pointless and unpleasant ad hominem - address the argument, not the argumenter. I think though it is worthwhile to set a standard for communication because that does involve real benefits. Conflating who and whom is never confusing and making a mashup of tenses rarely causes real misunderstanding. CAPS LOCK, refusing to use periods or capitalization, and giant, unformatted text blocks on the other hand are a huge impediment to comprehension.
The delineating factor, the thing that tells us whether or not we should correct someone or even dismiss their argument entirely, is whether or not they are easily understood. That last sentence is probably riddled with at least three separate errors in 'formal english' but everyone knows what I mean. If you can tell exactly what someone is saying then there is no need for correction "I ain't got no pencil" is perfectly understandable though it will make many people cringe. English is not a language that can possibly have a 'correct' version, if any language can, though many people of course insist that everyone speak exactly to the standards that were normal among their social group when they were young.