According to Kim Diehl, this instinct is the consequence of possessing the ability to manipulate an immensely vast and almost limitless energy known as Magic. Due to it's power, it often leads to destruction and therefore, beings that perform Magic innately are inclined towards destruction.
However, the kind of "destruction" for each individual varies. Among Witches, while some are prone towards outward destructive tendencies (such as blowing stuff up), others are more incline towards more "subtle" destructive tendencies such as emotional destruction (such as "breaking a man's heart" in the case of Tabatha Butterfly).
Although those who innately manipulate Magic are subjected to these forces, Death the Kid noted that those with this instinct can value even order and are not fundamentally incompatible with beings of order such as Death Gods nor are they true beings of destruction.