The Circle of Red - or Veneficti, as they called themselves - was an infernal sect of mages during the Dark Ages that believed that no knowledge should be forbidden and strove to achieve a state similar of God himself, whose designs in the world they perceived as flawed and constructed to capture the weak. To this end, they deliberately summoned demons from the Abyss.
Their philosophy: by denying the power of the Judeo-Christian concept of right and wrong, the Circle of Red performs calculated acts of Sin with the ultimate goal of complete control over body, mind and spirit. Sinning deliberately weakens the temptation that leads to spontaneous indulgence. Sinning repeatedly removes the power sin holds as a tainted pleasure or forbidden vice. Sin itself loses the power to gratify or instill guilt, and so becomes meaningless. Without sin, there is only choice and consequence, the fundamental essence of control. Absent any obligation to virtue or vice, Veneficti may work without the constraints of natural, or divine, order.
The Circle of Red mastered the subversions of the Divine Will, that is, the pillars of Abomination, which corrupt the patterns within the world to suit the will of the mage: Subversion, which seems to be a perverted form of Correspondence, Diabolism, which focused on summoning Demons, and Malediction, which focused on corrupting the truth into lies.