Lucifer, as all angels and men, is endowed by God with intellect. It is the intellect that allows us to make rational decisions which is free will. Your reason is free to choose God or to choose sin. So, the root of sin is in the free will. But without it, we would only be robots.
If you look at Genesis, the defining moment in serpant's delivery was the idea that even man can be "like gods." So, the driving force behind sin was a desire to be "like gods". If you look at Lucifer's reasons, it was the same desire."
The difference between us and satan is that fallen angels are condemned forever; we are not. There is no redemption for their rebellion and their fall from grace is permanent. Man, on the other hand, can be redeemed. But this redemption, just as our fall, must begin with a decision. Just as Adam decided to disobey, we must decide to obey. And just as Adam's fall would not have happened without God's punishment, our redemption cannot be possible without God's forgiveness.
Your reason is not driven by God. Your heart may be, but not your reason. That's why the crux of the faith (no pun intended here!) is love and not intellect.
Then why does every purely human man who has ever lived always chosen sin over God without His help? (For stuff like this, I'll just agree to leave Mary out of it :) It's 100% to zero, right? How can that be if free will could theoretically lead anywhere?
Why do you equate God's full control to our being robots? In the normal use of the word, robots are incapable of love and are not sentient beings. We all know that humans clearly are the opposite. As I have said, we truly do experience the free will you speak of, but it is God who is in full control, irrespective of our "wills".
Your reason is not driven by God. Your heart may be, but not your reason. That's why the crux of the faith (no pun intended here!) is love and not intellect.
There is good reason and bad reason, right? When we use good reason, where does that come from? From where is it driven? Ourselves? I would disagree. Anything with "good" in front of it comes only from God. Even if you say that we were born with good reason, where did THAT come from?