I don’t believe “a Christian can have anything they want”.
For instance, even if a Christian runs away from Jesus, I believe because of Jesus’ perfect sacrifice which makes a Christian righteous forever and God standing by his New Covenant by which he does not remember our sins and iniquities, they will still go to heaven.
Same with being demon possessed. It helps to know the truth because the truth is light and sets you free.
Hebrews Chapter 4 refutes the body of your comment.
As for the rest of it, I could not care any less. The only thing that concerns me is churches that spend a lot of time talking about satan and demons, without a lot of time talking about God’s grace and power.