The Doctrines of an Anti-Christ
Korihor was the third named Anti-Christ in the Book of Mormon (Sherem & Nehor were the other two).
Each of Korihor's arguments can be refuted. Later on we read how Alma refutes these arguments.
No Christ, No Prophecy
Korihor first taught that there would be no Christ (Alma 30:12). This argument is based on the premise that "no man can know of anything which is to come." (Alma 30:13) However, if no man including Korihor can know of things to come, how can he then know of things that are not to come? It's obvious that his purpose is to cast doubt on the fact that the Savior will come, but he does not think it all the way through. He simply accepts the teachings of the Devil's angel.
Must See to Believe
Korihor also takes a jab at faith. He claims that no one can know of things which he cannot see. To him, seeing is believing. But there are more ways to detect truth than just seeing. This reminds me of a talk Elder Scott gave with regard to this subject. He recounted a story about a man of little faith.
"Years ago I participated in the measurement of the nuclear characteristics of different materials. The process used an experimental nuclear reactor designed so that high energy particles streamed from a hole in the center of the reactor. These particles were directed into an experimental chamber where measurements were made. The high energy particles could not be seen, but they had to be carefully controlled to avoid harm to others. One day a janitor entered while we were experimenting. In a spirit of disgust he said, “You are all liars, pretending that you are doing something important, but you can’t fool me. I know that if you can’t see, hear, taste, smell, or touch it, it doesn’t exist.” That attitude ruled out the possibility of his learning that there is much of worth that can’t be identified by the five senses. Had that man been willing to open his mind to understand how the presence of nuclear particles is detected, he would have confirmed their existence. In like manner, never doubt the reality of faith. You will gather the fruits of faith as you follow the principles God has established for its use." (Richard G. Scott, “The Sustaining Power of Faith in Times of Uncertainty and Testing,” Ensign, May 2003, 75)
Management of the Creature
Korihor also taught that "every man prospered according to his genius" and that men in life fared "according to the management of the creature." He recklessly preached that "when a man was dead, that was the end thereof." (Alma 30:18)
If everyone were to play according to these rules, the law of the jungle would reign and chaos would ensue. There would be no order and the world would be in a perpetual state of war. It is in law and rule of order and reason that stabilizes society. Our Father in Heaven is the standard and He has taught man the law.
While spewing forth is garbage in front of Alma, Korihor accused Alma of "glutting on the labors of the people." (Alma 30:31) Alma took this accusation to task by plainly telling Korihor that he nor any of the other priests in the Church had earned one senine for their labors as priests.
The next refutation Alma makes is that Christ will come and that there is a God. He boldly testifies to Korihor of these truths. "I know there is a God, and also that Christ shall come." (Alma 30:39) Then he puts Korihor on the defensive by asking him for evidence that there is no God or Christ. To prove that there is no God is a much more difficult task than to prove that there is a God. Alma tells Korihor that all the priests testify of God and Christ as have all the prophets and all the scriptures. The earth and all the thing therein and the planets and the motions thereof testify that there is a God. (Alma 30:44)
Despite the insurmountable evidence, Korihor still desires a local sign that there is a God. He was granted his desire.
Alma, according to the power of God, struck Korihor dumb so that he could not speak or hear. (Alma 30:50)
It seems as though Korihor wanted to see a sign performed on someone else other than himself. The chief judge wrote to Korihor "In whom did ye desire that Alma should show forth his sign? Would ye that he should afflict others, to show unto thee a sign?" (Alma 30:51)
No, if Alma had performed a sign on anyone else, Korihor would not have believed. It had to be a sign Korihor could not deny in the least. Therefore Korihor testified saying, "I know that I am dumb, for I cannot speak; and I know that nothing save it were the power of God could bring this upon me." (Alma 30:52)
He asks Alma to life the sign, but Alma knew that Korihor was really not repentant.
Korihor is consigned to a life of begging before he is trampled to death by the Zoramites.
"And thus we see the end of him who perverteth the ways of the Lord; and thus we see that the devil will not support his children at the last day, but doth speedily drag them down to hell." (Alma 30:60)
Time and time again, we read in the Book of Mormon that disobedience to the commandments brings sadness and spiritual death, while faithfulness to the Lord brings life and happiness.
I trust Mormon's perspective. He had a whole civilization's history before him and thus could offer this simple, yet profound bit of knowledge.