I hypothesis that crystal sorcery in general dose tremendous harm to the users mind, not just the crystal catalysts. Big Hat Logan turned into a homocidal nudist when he unlocked the secret of Seath's crystal sorcery. That being said however, he also threw away his catalyst staff in favor of the Tin Crystallization Catalyst. Difficult to say if it had anything to do with his psychotic meltdown but it might have played a part. Seath The Scaleless was obsessed with immortality and more specifically the Primordial Crystal in which he claimed as his own after betraying his own kind. His research into the primordial crystal I strongly believe was the origin of crystal sorcery...which drove him insane in the end. (See the pattern here?) Without a doubt, crystal sorceries have a long history in being harmful to the users mind, be it both dragon or undead. One other note, it also seems to cause grotesque deformities, namely crystal like tumors to grow on the users skin. Seath was covered in them and his experimental subjects were also deformed. I wonder if this is why the Sage Brothers wear those plague doctor masks, so as to hide their deformities. Just an insubstantial theory but one to consider nevertheless.