The goal of a writer is to write something that others care to read. Correct grammar may or may not play much of a part in achieving this end.
As a student of foreign languages I will take vocabulary over grammar seven days a week. This isn’t to say that I don’t study grammar but if you don’t know a word no amount of good grammar is going to bail you out linguistically.
If you’re going to be enough of an jerk to correct someone’s grammar you had better be right 100% of the time or you are the biggest jerk in history. Even if you are always right that might not keep me from punching you in the neck. Grammar isn’t in itself communication; it’s simply a tool that can make communication clearer. Language is the wine and grammar is merely the glass. Sometimes people like to drink right from the bottle. Get over it.
I am a very firm believer in the Oxford comma.