Yes. That's my point. Belief in a deity. The theology/mythology consists of opposites:I've little to no idea about the others, but orthodox Christianity is certainly not dualistic. God is the sole deity. Satan/Lucifer is a creature. They are opposed but far from being equal.
God/Satan, Horus/Set, Marduk/Tiamat etc.
If you believe literally in the theology, you by default believe in the dualistic concepts of that religion, both gods.