Let's be honest, almost none of the Warcraft's famed evils was evil by their own free will.
Sargeras was corrupted by fel magic of the Annihilan and the Nathrezim.
Kil'jaeden, Archimonde and the rest of the Eredar were corrupted by Sargeras.
Ner'zhul later Lich King was corrupted by the power of skull of Gul'dan.
Neltharion was corrupted by Old Gods' whispers.
Arthas was corrupted by Frostmourne.

That pretty much shortens the list of "true evils" in Warcraft to Old Gods, Gul'dan and the Shadow Council, Cult of the Damned, Twilight's Hammer, Illidan and originally demonic races…