then lets say that he does exist id rather go with corrupting the humans "taking their souls to hell(his realm)"
From religious stand point of view id say he torture and do other bad things to the souls traped into his realm because:
-Hes evil so he likes to do bad things (torture) hes the prince of darkness.being neutral about devils or the humans would not make him the prince of darkness the true evil
-Because he punish the devils(his slaves,etc,men)and the humans (angels as well maybe...) hes the absolute when comes to evil there cant be a worse malefic ungrateful non~merciful entity(person,being)
-Because is fun for him,he enjoys it
-And ofc because he CAN.
Ow Ow and if you can't tell if someone/something is truly evil and can prove to the slightest detail that he did not had any right,reason for what it done/does/will do don't even dare to use that word you might be the evil one doing so
For example if you see a dark creature making strange noises and looks utterly ugly for you in the middle of night right in front of you and you call it monster and start trowing rocks to it with your friends(when that unknown creature might be in the pain of dying ,because of your religion teachings and your imagination that sure its a devil or satan)after you succeeded killing it I really wonder who's the devil.
Look ok. lets look at the most basic principal of Christendom, Islam, and Judaism. All is as God wills it. That means the bad the good, the dark, the light, the evil, the righteous. It is all him. They call the Devil the prince of darkness because god is the king. The devil, Satan, Lucifer, was banished from heaven along with a 3rd of the angles for a thought. In truth he the angelic spirit of music had a thought against his master and was punished. God gave Angles the capacity of free will and when they tried to use it they were banished from heaven. Heaven, our so called paradise, is a place lacking free will. Why will we go where our will cannot? I say all this because it was one my thoughts before I began my religious and spiritual journey that landed at Ancient Druidism.