The basis of the occurrence of evils are those desires which are acted upon and the orders that are innovated. They are against the Book of Allah. People co-operate with each other about them even though it is against the Religion of Allah. If wrong had been pure and unmixed it would not be hidden from those who are in search of it. And if right had been pure without admixture of wrong those who bear hatred towards it would have been silenced. 
(1) al-Barqi, al-Mahasin, I, 208;
(3) Idem., Rawdat al-Kafi, 58;
(5) al-Tawhidi, al-Basa'ir, 32.