Magic once seemed black and white. My teachers made it clear that you should not work with demons or dark gods and only needed to emphasis the light.  It pre-supposed that such black magic existed, but it needed to be ignored.  Concentrating on such forces was not only unbalanced, but it led you to all sorts of problems and mental instability.  Their case was re-enforced by the fact that the only people who apparently wanted to touch such magical systems were kids or those who were desperate to shock their parents.  The only notable advocates of such systems, such as Kenneth Grant and Aleister Crowley, were scary.  Systems also required the use of techniques which were pretty disgusting, with ritual