Their choice was freely made

In the chapter - The angels:
"The evil angels, in that first instant of their abuse of liberty, rejected God. Caught in a deliberate fascination of their own beauty, they refused to look at that beauty's source, refused to seek for happiness outside their own satisfying self; and so attempted to find in themselves what can be found only in God--the answer to the will's divinely given desire for goodness without limit. These devils can now sin all they like, and know themselves less free with every sin; the abuse of liberty mounts with each sin, the chains grow more galling, the self-imposed slavery more bitter, and the hatred more consumingly intense. Their choice was freely made, abusing liberty; and it is eternally confined to make up hell's most despairing torment."

St. Thomas Aquinas -- Summa Theologica