That's the first major disappointment for me in this game. Fallout 2 had it perfected back in the day. Where you would make a toon with 1 intelligence and he would actually really be so much of a [censored] that your only available social interractions were stuff like "Uugh??" "Me hungry" "*drool*" etc.
I can understand why they left it out, and the main reason is : Vocalized protagonist. They've already had to record tens of thousands of lines of dialog for the player character, imagine if they had to record several tens of thousands more to cater to all differing levels of intelligence + ALL the responses for all the counter actors in the game.... Jeez.
Back in FO2 it was easy since it was all written dialog, par a few exceptions like Myron (JET MOTHA[censored]A, JET!).
Still... A real shame, nevertheless :/