I have a few more thoughts to add (to many other thoughts) about what's wrong with the supposedly wonderful Plan of Salvation.
Don't Judge a Book by its Second Chapter
According to Mormonism (and a whole lot of other religions against which I harbor considerably less anger), after we die, we will be judged according to how we lived on Earth. Regardless of the verdict, this judgment will determine where we spend eternity.
Eternity is a long time, obviously. But regardless of how valiantly we may have fought against Lucifer during the War in Heaven before we were born, this life affects one hundred percent of our grades. Despite the fact that our mortal existence is a fleeting blip on our unending spiritual timelines, once you're assigned to the Telestial Kingdom, you're stuck there forever. There's no appeal, no negotiating, and there's no promotion to a higher kingdom because of good behavior. It's the equivalent of a lifetime prison sentence for possession of an ounce of marijuana.
God's decision to base our eternal fates on such a tiny data point is ludicrous--not to mention unjust. It's akin to reading chapter two of To Kill a Mockingbird and proclaiming that the entire book is crap. The best stuff is in the second half, but you'd never know that by focusing only on chapter two. You might even miss out on the good things about that section, considering you didn't bother with the beginning and might not completely understand what you're reading.
It's also unfair to us, the ones being judged, because even those few of us who follow the "right" religion have no way of precisely gauging where we stand in God's eyes (other than a Second Anointing, I suppose). Imagine getting a new job and never once discussing your work performance with your boss--or even meeting him at all--until he shows up one day to inform you that you suck and that you're fired. Obviously, if you'd known earlier what he thought of your work, you would have tried harder to meet his standards. But the way the Plan of Salvation works, you have one brief, blindfolded opportunity to hit the bulls-eye with the dart. It's not exactly a recipe for success or the brainchild of a being who could be considered just or merciful.
Political Upheaval in Heaven
The War in Heaven was, supposedly, a battle of ideas. Jesus had one idea and Lucifer had another. God sided with his favorite son and then executed a very Stalinesque purge of his political opponents. Simply for disagreeing with the man in charge, Lucifer and his followers were cast out of heaven and denied the possibility of eternal progression in every way. This is the equivalent of the death penalty for a first time offense of marijuana possession.
It would have been more merciful of God to compel Lucifer and his friends to comply with Jesus' plan. It would have been more understandable to have those who disagreed with him be born with the curse of Cain (yeah, I went there). It would have been better to simply take their defiance into account as one misdeed in a long existence of sins and virtues and let it be one of many things to consider in a judgment far ahead. But God decided to throw a fit and cast a third of heaven into outer darkness over one ideological difference.
Stalin killed hundreds of thousands of his countrymen. God damned billions of his own children. Who's worse?