If a kingdom is ruled legitimately and fairly (enough) by a lich?

[Beleriphon]

"Here's a form of magic that would triple the yield of crops and can be cast without drawbacks by 1/5th of the population... but I'm still going to present a society of landbound serfs under yearly threat of starvation, with 95% of the population involved in farming. Wait, you think I should include possible agelessness for people who aren't evil? That would make the setting totally illogical and destroy the moral fabric of the tale!"

In fairness immortality can be done in a few ways in fiction. You can go the undead monster with liches, vampires, and other assorted gribblies. All of them are monsters of one sort or another. One of other methods is being sufficiently awesome like the Eight Immortals from Taoist beliefs, who are immortal by virtue of being awesome Taoists. Eberron takes a third route with the Undying Court of Aerenal. They aren't undead perse and are created via some kind of religious devotion on the part of the elves where the court as a whole is effectively treated as a deity for the purposes of the game. Eberron also doesn't tend towards alignment absolutes for creatures (good red dragon, evil gold dragons for example) even if it uses the alignment system in descriptive rather than prescriptive way.

In comparison the lich is basically side stepping the whole learn how to do stuff and be meditative and calm to achieve a higher state of being, and just decide they'll do something horrific to gain immortality and damn the consequences.

I kind of like the idea that at least part of the ritual for lichdom involves tricking another person to willing take the lich's place in the after life.