2 Corinthians 11:14 "And no marvel; for Satan himself is transformed into an angel of light."
In 2 Nephi chapter 2, Lehi tells Jacob there’s a punishment affixed that is opposite to the happiness prepared for the righteous. If you're LDS and you think the punishment is Outer Darkness, you might want to reconsider.
For the rest of the chapter, Lehi teaches a dogma that points to Outer Darkness being the place of happiness.
In verse 11 he says, "For it must needs be, that there is an opposition in all things. If not so, my first born in the wilderness, righteousness could not be brought to pass, neither wickedness, neither holiness nor misery, neither good nor bad. Wherefore, all things must needs be a compound in one…"
In verse 13 he goes on to say that if there is no sin, there is no righteousness. For this reason, the Celestial Kingdom cannot be heaven. Where is the opposition and sin in the Celestial realm? It is absent. The people who go there get to spend eternity with their families in peace.
Outer Darkness on the other hand, is described as a place of weeping, wailing, and gnashing of teeth. What agony, what misery, what joy!
Still skeptical? What if I told you there’s no agency in the Celestial Kingdom? That's right, the thing you fought so hard for in the pre-existence, will be gone.
Lehi explains this in verse 16, "Wherefore, the Lord gave unto man that he should act for himself. Wherefore, man could not act for himself save it should be that he was enticed by the one or the other."
In context, Lehi is talking about the fruit of the Tree of Life vs the Tree of Knowledge of Good and Evil, but in LDS teaching this is an eternal principle. Agency requires that we be compelled by opposing forces.
Because there's no sin or evil in the Celestial Kingdom, there's no tension. Without opposition, it's impossible to gain righteousness and continue on the path to eternal progression.
The people who go to the Celestial Kingdom are damned for eternity, because they cannot progress. They revert to an infantile state of innocence, having no joy because they know no misery, and doing no good because they know no sin (2 Nephi 2:23).
The fall of man is directly associated with joy in The Book of Mormon. 2 Nephi 2:25 says, Adam fell that men might be, and men are, that they might have joy.
In the next verse, we learn that God's goal is to redeem us from the fall. Therefore, his plan is to eradicate our happiness.
Mormon theology ultimately portrays Outer Darkness as heaven, and Satan as the God of that realm. By taking 2 Nephi 2:25 to its logical conclusion, we learn that Satan also fell that men might be, and that they might have joy!
The opposition gospel twists the title of Adversary into a positive thing. It honors and glorifies Satan. If it's true, then it is only in him, and through him that we become holy. We must follow Satan to harvest true joy.
If you're LDS and you find this ridiculous, that's because it is. Yet it's what 2 Nephi teaches. If I may offer a solution, I implore you to embrace Biblical teaching instead.
Simply stated, righteousness does not need wickedness to exist. You do not have to be evil and miserable in order to be happy. The Bible draws a clear distinction between sin and holiness.
Romans 6:23 (KJV) says: For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.