Maxperson
Morkus from Orkus
And yet it says nothing about how you must roleplay when you have an Intelligence score of 5, nor does it say that anyone who doesn't do it the way you envision (which is based on some other game, it seems) is roleplaying wrong.
You're totally off-base here.
It says very clearly that int = the ability to reason. Therefore, high int = a high ability to reason and low int = a low ability to reason. You can go against that if you like, but you're going against the rules if you play a low int as a high ability to reason with a penalty.