I recently saw an ad for a Halloween party sponsored by a major corporation. The main tag-line of the ad was: "Evil never goes out of fashion." That line succinctly summarizes one of the major problems in our world - that evil does not go out of fashion. The love of evil is not new to our world. Thousands of years ago lived a man named Cain. His parents were illustrious - they were our first parents. Adam was a prophet of God; he and his wife Eve were a couple of the most chosen among all the sons and daughters of God. Some of their children quickly stopped following their counsels though. Among them was Cain who "loved Satan more than God" (Moses 5:18). Cain was not the first of Adam and Eve's children to leave God and love Satan: "And Adam and Eve blessed the name of God, and they made all things known unto their sons and their daughters. And Satan came among them, saying: I am also a son of God; and he commanded them, saying: Believe it not; and they believed it not, and they loved Satan more than God. And men began from that time forth to be carnal, sensual, and devilish." (Moses 5:12-13). After that time Cain was born. He became notorious when he killed his brother and lied to the Lord. Before he killed his brother Cain did not love the Lord. He was one of the most secular in a rapidly-secularizing world. He was Satan's protege.
Since that time, Satan's influence has continued to flourish. Satan is the father of all lies (see Moses 4:4), one who seeks to destroy the agency of man (see Moses 4:3) by deceiving them and leading them carefully down to hell. Satan likes to spread rumors and contentions. He enjoys being a troublemaker. What's more is that he enjoys the fact that not only do many people in today's world not believe in God, even more do not believe that Satan exists. If Satan, and therefore evil, does not exist then moral relativism reigns. Further, if there is no devil then soon people will believe there is no God. That is not to say that God only exists if Satan exists - that is not true; however, once people stop believing that there is absolute evil, namely Satan, they will soon stop believing there is absolute good, namely God.
Satan exists as no more than an abstraction for many people (the same could be said for their conceptions of God but it is my impression that more people believe in God than believe in the Devil). Many believe that They are nothing more than unknowable concepts and not visible percepts. Even more, because of mistaken beliefs about the nature of God, many cannot conceive of the existence of a literal devil. If God created everything, did He create evil (i.e., the devil)? If so, why? Does that make Him not all good? Many arguments continue on in a similar manner. We as Latter-day Saints have a much clearer understanding of how Satan came to be, even if our understanding is limited.