At first reluctant to kill, the vampire is finally forced into murder by circumstance or need - and killing becomes easier as the years pass. Realizing that she herself is untrustworthy, she ceases to trust others. Realizing that she is different, she walls herself away from the mortal world. Realizing that her existence depends on secrecy and control, she becomes a manipulative user of the first order. And things only degenerate as the years turn to decades and then centuries, and the vampire kills over and over, and sees the people she loved age and die. Human life, so short and cheap in comparison to hers, becomes of less and less value until the mortal "herd" around her means no more to her than a swarm of annoying insects. Vampire elders are among the most jaded, unfeeling, paranoid - in short, monstrous - beings the world has ever known. Maybe they are not demons exactly - but at that point, who can tell the difference?
"I want you to give them back, Flambeau, and I want you to give up this life. There is still youth and honour and humour in you; don't fancy they will last in that trade. Men may keep a sort of level of good, but no man has ever been able to keep on one level of evil. That road goes down and down. The kind man drinks and turns cruel; the frank man kills and lies about it. Many a man I've known started like you to be an honest outlaw, a merry robber of the rich, and ended stamped into slime. Maurice Blum started out as an anarchist of principle, a father of the poor; he ended a greasy spy and tale-bearer that both sides used and despised. Harry Burke started his free money movement sincerely enough; now he's sponging on a half-starved sister for endless brandies and sodas. Lord Amber went into wild society in a sort of chivalry; now he's paying blackmail to the lowest vultures in London. Captain Barillon was the great gentleman-apache before your time; he died in a madhouse, screaming with fear of the "narks" and receivers that had betrayed him and hunted him down. I know the woods look very free behind you, Flambeau; I know that in a flash you could melt into them like a monkey. But some day you will be an old grey monkey, Flambeau. You will sit up in your free forest cold at heart and close to death, and the tree-tops will be very bare.
— Father Brown, The Flying Stars