I would disagree entirely it seems to me that the claim that of sex and orgies at alleged black masses stems from the clergy's attempt to shock the followers. In dark ages era Europe sex and discussion or engaging in public of sex was shocking and greatly offensive to the social order. Thus to show witches, noncatholics, as doing so was to "prove" that they were evil or wild animals. So if the people are convinced that there "enemies" are unforgivable wretches then it's much easier to defend trying to wipe them off the face of the earth.
It's like Alice Cooper pretending to execute himself on stage, it's to be shocking. I don't see amy deeper meaning.