That is the problem of the game. The effect of Maddening Song does not match with the description.
https://divinityoriginalsin2.wiki.fextralife.com/Maddening+SongSing, causing characters in your target area to become Mad. Maddened characters will attack those nearest them, regardless of alignment. (Maddening Song now targets only enemy characters as of Patch v3.0.168.526)