I get tired of one dimensional villains and gray heroes. If I was going to run a game with PCs in the roles of villains or anti-villains, I'd want to have a plot where the goals of the PCs were potentially sympathetic. Magneto for example has a potentially sympathetic motivation - protect the racial and ethnic group (Mutants) he identifies with. His philosophy however - commit genocide before our enemies do the same to us - is decidedly unheroic, and his general philosophy of "it doesn't matter what gets broken or sacrificed on the way to the goal as long as we eventually get there" is one that is generally accepted as likely to become thoroughly depraved and evil. Redcloak in Order of the Stick seems to share Magneto's basic motivations.
The villains in my current campaign - Esoteric Order of the Golden Globe - are (I can now reveal as spoilers) trying to create their own small copy of the sun, in order to be able to bring warmth, light, and healing where they feel that the gods have unjustly withheld it. And they feel that this ideal world where humanity will have unlimited healing and light at their disposal is such a good and noble goal, that it really doesn't matter what gets broken on the way. Afterall, once they have the unlimited power of healing and creation, they can always fix it.
I haven't watched it, but I understand that there was recently a show on television about a dying man trying to create economic security for the family he was leaving behind... by dealing drugs.
If I was running an evil campaign, I'd either want to offer a 'redemption plotline' that forked off the main plotline where the villains become good guys, or else I'd want to make the focus of the campaign characters that had some sympathetic motive and see what obtaining this 'good' would be like if you tried to obtain it by utterly ruthless means.
Idea #1: The PC's are collateral damage in the aftermath of a 'good wins' campaign.
Good has triumphed. The Good Heroes have defeated the Evil Tyrant, scattered his armies, overthrown his priests, and killed his necromancers. They now rule justly, fairly, and mercifully over the defeated people that they have liberated, bringing with them strange new ideas like universal education, sanitation, and equality before the law. New social structures are being overturned - slaves are being set free without payment or recompense. New worship practices, like bathing are being encouraged, overturning long held pious worship of the god of filth, the mistress of sin and vanity, and the god of tyranny and might. But nothing is perfect, and no victory comes without cost. The new rulers are insufferable in their overbearing insistence that they are right and everything else is wrong. New racial groups are moving in, and old social orders are being upended. The conquerors are encouraging colonization by members of their own ethnic group and getting a fairly large share of the spoils of power and wealth, and not all their agents are perfectly just - much less perfectly diplomatic. There is a tendency of the conquerors to do a lot of outright smiting of things they don't like and they aren't very open to new ideas. Also, there has been a lot of what you might call - collateral damage. Orphans, widows, widowers who lost loved ones in the war. People whose trades and livelihoods which were once noble and of high regard, are now destitute. Families that were highest in the old social order, now find that they are often the lowest. And people who are once proud of their national identity and their unique culture, are finding it all just slipping away, as their nation gets slowly assimilated into someone else's culture.
Well, the PC's do not have to stand for that. Each has a legitimate grudge against the new order, and they are determined to see it destroyed. And they are not alone. Tune the setting to whatever you like to make overturning the new order as sympathetic or as blatantly evil as you like. Depending on how you want to play it, you can play up the imperial colonial tropes of conquering power, or their relative enlightenment and benevolence compared to how things were before. Or both.