The cause of evil is ignorance. Being ignorant of right words and behavior, one has no choice but to say wrong words and act wrongly. Moreover, when one does wrong words and actions for the pursuit of one's own desires and pleasures, he/she continues to say wrong words and actions because he/she is ignorant of what misfortunes the words and behavior would bring.
Almost every human being is ignorant of his/her own ignorance. They don't know the fact that they don't know. Don't think you'll be an exception just because not everyone does. You don't know that you're ignorant.