During my journey out of Mormonism, I briefly courted the idea of reverting to regular Christianity. (Mormonism is a form of Christianity, although it is a topic of heated debate as to whether the church sufficiently focuses on Jesus.) This may have lasted a month or so.
But I found Christianity to be almost as easily dismissible as Mormonism. (And this was before I read books about how the New Testament was compiled and who the historical Jesus actually was.) Christianity, as I understand it, relies on a central premise that all of us sin and thus become unworthy to be in God's presence. To remedy this, we have to repent and forsake the sins. But for some reason, the Christian God either cannot or will not forgive sins without someone else suffering for them. And that's where Jesus' suffering and death come in. Apparently God needed to punish Jesus (or himself, if we're supposed to make any sense of the trinity) in order to be able to forgive mankind their sins (including the "original" sin of Adam).
If this is true, that God cannot (or will not) forgive sins without punishing someone innocent, then what does that say about him? Perhaps that he is petty, immature, cruel, and unjust? How is it that God, the all-knowing, all-powerful ruler of the universe, requires the punishment of an innocent person to "atone" for the sins of others? Why can't he do what we regular mortals do all the time: forgive and forget. Or, if a law has broken, sentence the wrongdoer to a punishment that is proportional to the wrong, and once the sentence is served, he/she goes free. If you wrong me, and then ask for forgiveness, I'll probably give it to you (depending on the wrong). Maybe I'll require you to make some sort of recompense in the process, but hey, that's fair, right? What I won't do is take out the "pain" of your wrong on some innocent third person, like my neighbor or my dog. If I can forgive without making anyone else atone for the "wrong," then why can't God? If God is concerned with our sins, there is nothing preventing him from just telling us the right way, and then independently deciding to forgive us (and/or punish) when we do wrong. No middleman necessary. Because Jesus is thus unnecessary, I don't believe he is a "savior" of anyone.
Mormonism tries to explain the need for an atonement by claiming that God's justice cannot be "robbed" by mercy. Apparently, there are some cosmic laws of justice God is subject to that not even he can abrogate. But in that case, God is no longer omnipotent, and how can we trust that he'll be able to "save" us at all? The Mormon explanation also seems to ignore the question of why God can't simply satisfy justice by punishing us directly and individually for our sins. Would that really be so hard?
That's the first problem I see. The second is hell. Traditional Christianity teaches us that hell is a place of endless torment for those who sin or don't believe in Jesus. Setting aside the criteria that determine whether one goes to hell or not (which I think is an unnecessary discussion, given the following), consider the concept of hell itself and how it squares with a just God. Our mortal existence is indisputably finite. But Christianity would have us believe that our souls will live forever. Therefore, being sent to hell represents an infinite punishment. That means that an infinite punishment is inflicted for actions/thoughts which are, by necessity, finite. That doesn't match up. If there is some system of morality that dictates the gravity of "sins," then theoretically there should be some corresponding system of punishment commensurate with the severity of such sins. It doesn't matter what sins you committed during your lifetime. Even Hitler's atrocious actions, while incomprehensibly abhorrent, were still finite. Thus, not even he deserves an infinite punishment. Surely there would be some punishment that would be commensurate with his bad acts. Maybe it requires him to suffer in hell for an equal amount of years as the cumulative amount of life that he took. God could figure out a proper number (he's all-knowing, after all). What is certain, however, is that a just God could not possibly sentence someone to any degree of infinite punishment for wrongs that are, by definition, finite. Thus, traditional hell is out of the question, and so is traditional Christianity.
Again, Mormonism tries to get around this obvious injustice by creating the three degrees of glory and then outer darkness. But that really doesn't solve everything. First of all, outer darkness would basically be the Mormon equivalent to Christianity's traditional hell. So again, if anyone goes there (indefinitely) for deeds done in this life, it flies in the face of justice and must be rejected. Also, the lesser degrees of glory don't really solve the problem, either. Mormonism believes that once you're sent to one kingdom, you cannot progress to any other. Thus, you are essentially "damned," in the literal sense of the word. It makes no difference that apparently the lesser kingdoms are still places of glory and wonder. They represent an infinite punishment for thoughts and actions done during a finite existence.
So there you have it. Two of the central doctrines of Christianity are faulty. It seems perfectly clear to me now, but when you're caught up in the system, you don't think to critically examine fundamental doctrines in this manner. In the Mormon church you'll hear people talk about how the atonement is such a mystery and is difficult to comprehend. The reason for this is, presumably, that it's such a deep doctrine. Well that's not the case at all. It's difficult to comprehend because it doesn't make any sense. It's counter intuitive. It doesn't match up with our real world experience. It's nonsense.