I bet you prefer to play all games in God Mode.
While feared, the one thing you are thinking is to protect yourself, so either running away or going completely defensive are your options - blocking, curling up in a little ball shielding your face and torso. Fear makes you want to run and hide and if you can't run, then hide behind your shield. So, yes, blocking while feared makes perfect sense while pausing to take a nice cool drink really doesn't. So, if you are feared, try being logical and Run Away or Shield Block till it is removed or goes away.
Rage - madstone or otherwise - makes you into a raging maniac heck bent on destroying everything in your path. While Raged - ie Berserk - you are not thinking about healing yourself or removing curse or anything else. Rage should make you immune to charm, fear and anything that would make you compliant. The cost of having all that extra strength, hp, speed, crit range, etc, is that you don't have the mental capacity nor desire to take care of yourself. Well, actually your Character doesn't. You, the player, may really want to heal your character, but this is a ROLE PLAYING game, so you are playing your CHARACTER and a Raged character won't think to heal himself.
As far as game mechanics go, yeah, being able to have your character drink a potion while feared or raged would be really handy and make it a lot easier to solo and do without any other class along to help out... but it would ruin the RP part of the mmoRPg as well as the TEAMWORK part.