What is it with certain Christians treating every movement or idea they disagree with as a religion?
Because it puts them on equal footing. Until said Christian plays the "It's not a religion, but a relationship" card, which implies that Christianity must be treated separately and by different rules. Plus...
(those of you who know formal logic...I apologize. My heart is in this, but my knowledge is not. If someone wants to correct this, feel free to do so)
Proposition 1: Anything based on lies of the devil is satanic rebellion.
Proposition 2: All religions that are not Christianity are lies of the devil.
Conclusion 1: Therefore all non-Christian religions are satanic rebellion.
Proposition 1: My interpretation of scripture is correct in God's eyes.
Subproposition 1: Therefore, disagreeing with me is disagreeing with God.
Proposition 2: Disagreeing with God is satanic rebellion.
Conclusion 2: Therefore disagreeing with me is satanic rebellion.
and, to wrap up -
Conclusion 1: All non-Christian religions are satanic rebellion.
Conclusion 2: Disagreeing with me is satanic rebellion.
Overall conclusion: Disagreeing with me is promoting a non-Christian religion.
Implied conclusion: Disagreeing with me is promoting Satanism.
...and that makes it much easier to demonize people you don't agree with.