The biggest point I can make on this topic is that we know SO LITTLE about what pre-earth life. We have little peaks at it here and there, but it is not something we can really make solid judgements and statements about. God seems to reserve revelations on different planes of existence for those existing in those planes.
why is this? Because our duty is here, not there. There won’t be a satisfactory explanation because the required information to make it doesnt exist.
That being said, this is a forum and we can surely talk about this, and I think some insights can be gained from such a conversation
Is my 3 year old unclean and unfit for God’s presence when he hits his sister? Of course not! Like Adam and Eve and all others under the age of 8, he isnt accountable for these decisions because he hasn’t been fully taught, nor is he even capable of understanding. But, as his father, I don’t look upon this act with allowance, no, I teach him, I discipline him. I do what I can to teach him how to be good. That doesn’t mean I kick him out the door and tell him to come back when he is righteous. Same with God. He doesn’t look on sin with allowance, but that doesn’t mean we are removed from his presence when we fall short.
I believe whole heartedly that the affects of the atonement are all encompassing and can reach back to pre-mortal life.
As for sin and uncleanliness in pre-mortal life, for the purpose of my explanation, there are three types of motivations that lead us to do wrong. weakness, pride, and rebellion. God’s grace covers weakness and pride so-long we are trying to grow, but rebellion is the motivation that keeps us out of God’s presence.
The third of the host of Heaven seemed to be the group that rebelled. Rejected Heavenly Father entirely and all that he offered.
At the end of the day, the gospel, the purpose of life, and all that we are here to do has everything to do with what we want. God provides some options, we pick which one we want, and we are blessed/cursed with whatever else comes along with that decision