Actually, the major victims of Touch of Idiocy are those who have a lower Int to begin with, particularly rogues and clerics.
Take Bill the Cleric, with 10 Int. Two ToIs with good rolls take him down to 2, sub-sentience. Bang goes his spellcasting (too stupid), strategy (too stupid), wand usage (too stupid) etc.
Or Joe the Rogue, with 12 Int. Two ToIs with lucky rolls take him down to 2, again, sub-sentient. Out flies his hit-and-run strategy, his sneak attack, intelligent usage of skills, etc.
Sure, it will hit Bob the Mage as well, but the major strategic usage I would argue is to reduction below sub-sentience, not just an erosion of DCs. I guess the lucky one is the barbarian, who didn't really use much other than hit-the-enemy-hard-with-a-big-stick tactics anyway
