In general a Lich is an abomination against something that is holy and/or natural. So if you world has more natural deities then the defiling of nature and innocent creatures. If your world is more Elder and Spirit based then the trapping of old souls and the consumption of new ones. Or if the world has more Divine and Holy Deities, that things like love, joy, peace, patience, kindness, goodness and self-control must be defiled.