What constitutes evil? What is the difference between "good", "bad", "love" and "evil"? These are philosophical questions that man has been trying to answer since St. Thomas Aquinas; and long before him.
Good, bad, love, and evil are relative terms, and only apply in the worlds of duality. These terms are also subjective in the sense, that what is good in one culture can be seen as bad in another; the same with love and evil. With this in mind, we shall try to define good, bad, love, and evil in spiritual terms.
Good is any action that does not encroach on another person, or do harm yourself. It may, or may not benefit another; but it does not harm them. Holding doors, mowing the lawn, being pleasant to other people, and going to church are all good by this definition.
Bad is any action that hurts, or causes a negative effect on another. Hitting, gossiping, vandalism, and robbery are bad by this definition.
Love in the spiritual sense, is giving to another without thought of reward, or gratitude. Love is altruistic in nature, and shown through demonstration. Real love cannot be expressed in words. Real love is demonstrated by one's actions. A parent's bond with a child, the miracles of Jesus, giving one's life to save another's, and sacrifice are all love by this definition.
Evil is achieving one's own desires no matter what the cost to others. Evil is self absorbed, and egotistic in nature. Evil has no regard, what so ever for anyone else, only for its desires. Murder, rape, tyranny, and black magic are evil by this definition. Satan is the embodiment of true evil in this world. It is inconceivable that anyone would choose to worship him. The true manifestation of evil is incapable of love, how could these souls believe that he will return their adoration?
As stated above, these terms are relevant only in the worlds of duality, the physical, the astral, and the mental. When one goes beyond these worlds, there is only love. Our problem is traversing our path through these lower worlds until we have earned the higher ones.