“profanity and obscenity entitle people who don’t want unpleasant information to close their ears and eyes to you.”
Same thing with bad spelling and grammar. It entitles people to stop listening to you. I think that if you don’t understand the difference between then (an expression of time) and than (a comparison) I don’t have to listen to to you. Also, if you say would of, could of or should of, I’m not listening to you.
If you want to be understood and takes seriously, especially in business, learn the basic rules of English grammar.
Copyblogger has this to say: