I honestly don't believe in the version of Satan who is a fallen Angel working in opposition to God. If there is a Satan, I believe that it is a side effect of God's desire for free-will. In that way everyone accidentally serves Satan unintentionally sooner or later. No one is perfect.
Respectful Question: Does Fundamentalist Christianity believe that anyone who denies Jesus Christ as LORD and savior is a partner with Satan?
I cannot speak for all, but I can speak for myself.
No, though we all can be used and manipulated by him. A Christian is aware of the trap and has tools to defend himself, though it can be difficult at times.
Others, not knowing of the trap, are more likely to get caught.
Satans greatest accomplishment is convincing people he doesn´t exist.
With respect, if you believe satan is not as Christ and the Apostles described him, what other parts of the Bible do you choose to jettison , and why ?