A perverse nature can be stimulated by anything. Any book can be used as a p-rnographic instrument, even a great work of literature if the mind that so uses it is off-balance. I once found a small boy masturbating in the presence of the Victorian steel-engraving in a family Bible.
If he can only perform good or only perform evil, then he is a clockwork orange - meaning that he has the appearance of an organism lovely with colour and juice but is in fact only a clockwork toy to be wound up by God or the Devil.
It's funny how the colors of the real world only seem really real when you watch them on a screen.
The important thing is moral choice. Evil has to exist along with good, in order that moral choice may operate. Life is sustained by the grinding opposition of moral entities.