Is there any major differences with using a stupid character? As far as I know all could do all the quests being stupid. The only difference is the journal entries, conversation options, and what you teammates with voices say when you first meet them. Any MAJOR differences?
Some quests aren't avaible, such as the HO island quest, and other "intelligent" quests. And you can't use magic. At all.
Your tech skills would be limited to. If your going to play a stupid character, you should go all the way and make him ugly and half-orc as well. And get a sharp sword.
Next thingyou know they'll make a Tourrets Syndrom character..... "Yes Virgil, I do believe that is the best course of.....FUCK SHIT POON!....action at this given time!"
If your background is idiot savant you can have a stupid mage character. But personally its just a great way of making Godly inventions and still being an imbecile juuust like in real life. Look at rain man vs Predator wow what a great film.