Well, its less about impending doom and more like "be careful" and "don't abuse your power". Be it arcane study, tapping into your subconscience/training, or turning to your deity. It screams "magic is not a toy".
There's a reason king's train guards and not warmages... lol! I believe it'll only bring down the casters by 1 or 2 tier levels. Not sure if it would hurt semi-casters more or not. They're already pretty weak. (Like the paladin/bard) And in some ways, it doesn't cause they get just as much sanity as say, a wizard. And don't need to rely on spells quite as much as a wizard... Paladins especially would notice the buff as their divine grace increases saves across the board, insuring their san checks are a little less dangerous.