How can you have free will and yet be under the rule and control of someone else? That's like saying a prisoner in solitary confinement has freedom to come and go as they please. If something controls you, do you really have a choice in the outcome?
And if Satan is so bad, in the book of Job, Satan (in Hebrew means adversary, accuser as in a prosecutor) acts on behalf of god and in defense of god's plan. How does a rebel angel who made war against god to create death and hell before the events of Eden then turn around later to switch sides and be god's prosecutor and tempter against poor ole' Job?
As for knowing the bible, many atheists and non theists say the same of christians.