Slavery was the factor - as stated by the rebellious states themselves as they mounted their insurrection. It is undeniable no matter how many times it is protested. The slavers saw the writing on the wall and instead of preparing for the inevitable, chose rebellion, insurrection, and war.
I have no particular problem with lee - he was a fine tactician. He was also a turncoat who dishonored the country of his birth.
You mean Virginia?
You have to consider the situation in the context of the time. The devotion to one's state above all else was very strong.
A respect for all the suffering, and dignity, and grace (something familiar to us nowadays from tabloids and talk shows, yet somehow connected to deeper emotions with ancient, mythic sources) prevented people from asking too many hard questions about his actual loyalties, commitments, and decisions.