Demons Yes, the Devil No (?)

Demons - they are more believable than the Devil, the Rebellious Angel.
 I mean, How can an angel rebell against God?
He would have to be really stupid.
The closer you are to God, the LESS likely you are to be stupid.
For the intelligence of God is absorbed by being in His Presence, OK?
Can the planet Mercury suddenly just drift away from the sun ?
Not with all that gravitational pull !!!  
Well, with the "pull" of God acting upon the angels, how can they rebell?  
Case closed. No, I doubt the reality of a personal Devil.  

But demons are another can of worms entirely.
The original meaning - before the revisionist version given  in the Bible -
was HUMAN spirits after death. As opposed to fallen ANGELS.
I can see demons as merely human ghosts.
"Unclean spirits" the New Testament calls them.(Luke 11.24-26).
Which should mean that they are not saved. They are damned?
If so why are they not locked up in the prison called Hell.
If the saved are in heaven and the damned are in hell,
then why are there ghosts wondering the Earth ??
A third category, obviously.

Maybe, they are saved enuff to be acceptable in heaven
but they just feel like holding onto the past, this world.
Sort of like a traveler in a bus station who has a ticket.
But, instead of going forward to his destination,
tarries at the bus station for a few days.