Universalism teaches that all people will ultimately be saved no matter what they believe here on earth. You could deny God, hate Him, blaspheme against Him, join a satanist group and murder people and still go to heaven.
Bible-based, non-Christian cults are those groups that claim to be Christian, use the Bible, yet have redefined God, Jesus, and the gospel sufficiently to make salvation of no effect. Part of CARM's purpose is to refute error and teach the truth so that people will not go to hell. Universalism is definitely in error, which needs to be addressed.
Let me take Mormonism, for example. Is Mormonism wrong? Is it dangerous to the soul? Does it lead to damnation? The universalist would have to say no, even though Mormonism teaches that god came from another planet, has a goddess wife, and that we can become gods (obvious false teaching); universalists teach that Mormons go to heaven. Of course, universalists who claim to be Christain might assert that Mormon theology is wrong. But, they would also maintain that in the after life, they would be able to repent and follow the true God. Logically, then, we could make the case that the universalist would encourage the spread of Mormonism since it has good morals.
Mormonism is not Christian. It is false. It is a compilation of lies from the devil. It damns people for believing in a false god, a false gospel, and a system of works-righteousness that is supposed to help them become saved. But, to the universalist, such heresy amounts only to a goof, an error in judgment, with the ultimate result being heaven. It makes no difference if a person is a universalist, a Mormon, a Jehovah's Witness, or an orthodox Christian since they are all going to heaven according to universalism.
To a universalist, there would be little or no need to refute Mormonism. Why? Because what is the universalist going to warn him about? Damnation in hell? Not at all. Rather, he'd have to threaten him with heaven! Instead, the universalist is more concerned with converting someone to "truth of universalism." In so doing, they endanger the souls of all whom they contact.
Let me illustrate this with a Universalist witnessing to a Mormon:
Universalist: "Listen here Mormon, if you continue to believe that you can become a god, that Satan and Jesus are literal brothers, that God has a body of flesh and bones and has a goddess wife, and that you can become a god of your own world, you know what is going to happen to you? You're going to heaven! So there!"
Mormon: "Sounds good to me."
So, where is the power of universalism to correct Satan's lies? Does it carry a warning for those who serve false gods except to say that it isn't nice to believe such things as Mormon doctrines? But, so what? It doesn't matter; Mormonism, and other cults, would lead to heaven.
Is there orthodoxy in Universalism? Does it have the power and right to refute the errors of the cults? I don't see how. But, I do see that it is dangerous.