only people who don't deserve to go to hell can become demons. it's only through god's grace that the sinful people on this planet are allowed to live another day and not rot in hell. Only a person who has made it to the very end without giving up can have the right to trample all over humanity. That person is a demon. It's a misconception that demons are evil like you. All demons were once angels and they retain those good qualities. The only issue is they have a problem with the divine order and life itself. That they are allowed to exist is only because god must concede to their righteous grievances.