When it comes to discussing your opinions about something, spelling out your words, and using correct punctuation is generally viewed as a common courtesy to those people who will be reading what you write.
If you're making a three word reply, then do/type whatever you want, because most people skip over those posts without so much as a glance. However, if the post exceeds three to four sentances, at least throw a period or two in (where they belong
confused ) to separate your thoughts.
Theres a big difference between ignorance, stupidity, and simply being too lazy to type out your words.
I for one tend to have enough respect for my thoughts, and those who will be reading them, to type my words out completely, capitalize, use proper punctuation, etc. etc.
Not because I feel that I'm some high-and-mighty grammar nazi, but because I appreciate a well worded and thought out discussion.
As for someone who shows up typing 'sentances' where entire words are replaced by single letters, the occational number shows up, and I see the terms 'LoL', 'WTF', and 'STFU' more than three times in rapid succession generally gives me a pretty good idea on that persons maturity level, and a decent shot at geussing their I.Q.
In short, yes, bad grammar can be used as an insult, if for no other reason than to call a person too lazy to care about how they present their thoughts to the rest of the
planet.
Later.