The "adventurers" (i.e. player characters) literally narrate the trailer of MoP, the Adventurer (i.e. player character) is indeed an acknowledged story character, meaning that there are also Shadow Priest adventurers who are seen as heroes and don't succumb to madness.
This is a silly argument. Yrel went mad with the Light, the Scarlet Crusade went mad with the Light, the Botani are mad with Life, those who created Mana Bombs are mad with Arcane, etc. There will always be people who abuse such powers, and you can't even make the argument that there are more people abusing the Void than any other power, given how Draenor was taken over by Light fanatics in BfA.Yet. Benedictus has. Deathwing has.
If such powerful beings go mad because of the Old Gods, playing around with their powers is sheer stupidity.