Why?

What motivates fictional villains? Aycharaych tells Flandry that he serves the Merseians in order to prevent them from ransacking Chereion, destroying his heritage and directly using Chereionite instrumentalities:

"'...would you let your war lords turn these instruments to their own vile ends? No!'
"And Flandry understood."
-Poul Anderson, Sir Dominic Flandry:The Last Knight Of Terra (New York, 2012), p. 600.

However, there is ample evidence that Aycharaych enjoys what he does. He even acknowledges but tries to make light of this:

"'Oh, true, an art, a sport - yours too...'" (ibid.)

- condemned out of his own mouth.

There are too many other great villains to list here. James Blish's Theron Ware conjures and controls demons in order to gain knowledge whereas his client, Baines, the arms merchant, is an aesthete of destruction. Two compelling demonolators are CS Lewis' Frost and Wither. Hannibal Lecter is intelligent, perceptive, charming and resourceful, qualities that would be good in anyone else. Anthony Hopkins has played both Lewis and Lecter!

SM Stirling's Count Ignatieff is another cannibal and believes that he will go to Hell - as one of the torturers.