grammar and intelligence are not mutually exclusive.
many Mensa members speak gibersih, are they idiots?
what would you think of a guy like Stephen Hawking, if you had never heard of him and met him after his battery in his speech/typing PC assistant had died? would you consider him an idiot too?
First and foremost, I would think there's something physically wrong with him, as anyone would.
That you would compare Hawking's medical condition to one's inability or refusal to respect their brain is the real insult.