From a mythological perspective, why does our religion have such a powerful and detailed “Sons of Perdition” 
element? I asked myself this recently after observing other members talk about this theme in length during separate conversations. They were so passionate about discussing this state of being, going on and on about it, even though it was only tangential to the conversation at hand. I watched them go deep within themselves as they pulled out all the information they knew about Sons of Perdition and reviewed it out loud. It prompted me to ask myself “why is this important to them?” They were emphatic about how difficult and rare it was to reach a level of knowledge and spiritual enlightenment that one could even make this conscious choice. If it is nearly impossible to become a Son of Perdition, why does it matter?
The conversations were about being worthy, losing faith, and failing to do “all that we can do” to enact our own salvation. I no longer agree with many traditional members’ views on life being the ultimate, high stakes pass/fail final exam. So maybe that is why I was so intrigued by their focus on this topic. In our religious mythology, we have 3 main kingdoms of glory. These have nice tidy definitions and names. Unlike many other Christian denominations who focus on just heaven versus hell, saving people from eternal damnation, we are focused on making sure we get the biggest prize. After all, 2nd place is first loser right?
I think one part of the reason Sons of Perdition exist in our mythology is that the actual conditions of Celestial glory are not well defined. Yes, we know we inherit all that God has, but what exactly is that? We can’t comprehend this state of being. We don’t know what the prize really is, except for vague ideas that it is the best we can get. We become gods with the power of eternal lives, but we don’t know exactly what that means or how it happens. This leaves a nebulous sort of feeling.
Another problem of life with such a risky, one-shot chance at the reward is perfection always seems to slip out of our grasp. The root of the problem lies in the checklist. It is endless and overwhelming. There is always something you could have done just a little bit better, if only you had enough faith and willpower. Even the most fundamental and literal member senses this deep down I think. No matter how much they do, or how hard they try, it can’t all be done. Satan is waiting for them to slip up and fail. Did they maybe forget to read their scriptures this morning? Did they only have a half-hearted family home evening last week? Did they not include the monetary value of company-paid benefits in their tithing calculations? All of these are a lack of perfect obedience and effort.
Here is what I saw: Sons of Perdition make a convenient floor, a lower boundary to our possible life results that we don’t really have to worry about crossing. We don’t know what it means to become a god. At least we can clearly define the worst-case scenario. I might have an occasional immoral thought, skip a meeting at Church, or miss a home teaching family one month; but at least I know I won’t deny Christ and become a Son of Perdition. They have to REALLY try hard to be evil. I am doing the best I can, but I fail sometimes. At least I am not THAT!
I think it might be a convenient way for people to compartmentalize their perceived risk. Sons of Perdition are a tool of comfort in a way. It helps us deal with processing the loss of a loved one who leaves the Church. That is what I heard several times. “Those people lost their faith and became apostates, but they didn’t know enough to become Sons of Perdition.” If they knew better, they would come back. They are safe though. They won’t end up in the Celestial Kingdom, but they also won’t end up in Outer Darkness. It’s going to be ok.
Just as an interesting tidbit of trivia, it was not always clear if there will be Daughters of Perdition or not. Brigham Young in his classic style of being on the wrong side of modern sensibilities firmly declared that women were not capable of achieving perdition status. Fortunately, this right was later restored to women by Wilford Woodruff. So don’t worry about issues of equality in outer darkness 
[Reference: http://en.wikipedia.org/wiki/Man_of_Sin]