Nehor started a movement that would continue to threaten the peace and stability of the Nephite nation for a long time to come (Alma 1). This was a religious movement - a movement of ideas.
In Alma 2, Amlici begins a secular, political movement that further threatens the nation's peace when he attempts to overthrow the system of liberty and self-government and replace it with a king (himself, of course). According to the account, he was a "cunning man" and a "wise man as to the wisdom of the world," and he was a member of the order of Nehor (Alma 2:1).
The Nephites rightly feared that if he succeeded in making himself king that he would put down faith in Jesus Christ and further establish his own philosophy. The idea of the Nehors was simple. Nehor taught "that all mankind should be saved at the last day, and that they need not fear nor tremble, but that they might lift up their heads and rejoice; for the Lord had created all men, and had also redeemed all men; and, in the end, all men should have eternal life." (Alma 1:4) That idea -- that men and women can do exactly as they please without eternal consequence -- is at the core of many movements then and now. People are not personally responsible for their actions and can live as they please without restraint. But eternity imposes consequences on all of our actions. We can't avoid it.
We are eternally accountable for our choices and behavior. What we do matters. If all men would humbly follow Jesus and keep his commandments, they could live in peace and happiness. Alma clearly described the consequences of following the teachings of the Nehors (Alma 1):
32 For those who did not belong to their church did indulge themselves in sorceries, and in idolatry or idleness, and in babblings, and in envyings and strife; wearing costly apparel; being lifted up in the pride of their own eyes; persecuting, lying, thieving, robbing, committing whoredoms, and murdering, and all manner of wickedness
That course led to poverty of spirit and body. I have seen the same pursuit of worldliness destroy people.