Why is Litany evil? Reaping I can definitely see the argument, but Reinforcement?
Far as I know, it's not even confirmed that they're powered by hymns in Hell.
The Litanies themselves aren't evil, but have some inhuman incentives. Reaping's only the most obvious of the bunch.
Reinforcement pushes you constantly to become more transhuman. The more you progress, the more certain things seem justifiable. Reinforce yourself to not need sleep; then not need food, and so on. Then eventually, you do not need anything. Boom, you're no longer reliant on society or empathetic connection to your fellow man! In a relatively good case, this means you'll become an ascetic monk pursuing eternal self-perfection. This is maybe the mildest, but there's enough space for malicious gradients; some conceited bastard might start to self-perceive as a perfect being. There have been documented cases of Reinforcers praying to themselves or their future selves. That can have nasty results.
Reassurance is something I often think of as the scariest Litany because it's based entirely on the power of lies subsuming truth. Ancient Reassurers can bend the world as easily as they bend minds. Even relatively innocuous cases (a Reassurance theme of, say, "isekai protagonism,") are able to completely brainwash you into an adoring slave, because an isekai protagonist has a harem, doesn't he? In even worse cases, you can have Reassurers based on fear who saturate an entire town in their theme and make it a literal nightmare to live in, forcing people to obey or else.
Reciprocity's the Litany of physical and
social connections - if you can't think of why that has some nightmare fuel potential, take a moment. It propagates effects like nobody's business. Making Reciprocal zealots is easy, as is becoming a lich via binding phylacteries. You could bind yourself to an entire populace of mind-slaves and force a potential assassin to slay thousands before you can be put down like the rabid dog you are.
Then you have Revelation. It's sometimes said the Lord Revelator is the only being with true free will in the Dominion. This assertion's not accurate, since the Lord Revelator has fellow Lords and Ladies, and some Ancient contemporaries who retain sufficient hold over reality. Still, he's most likely got more freedom than anyone else. If he can play puppeteer with Ancients, then even mortal people are nothing in the face of a common Revelator. All it takes is one sour look at a cafe to trigger their ire, and a Revelator can turn your next year into a living nightmare with a whispered prophecy.
And finally, Repulsion. It's the Litany of banishment and warding; admittedly, this one's the most difficult to bend to inhuman or immoral incentives or wills, but you could still do something like banishing your own humanity or other essential aspects of selfhood until you eventually lose them entirely.
Like I said, it's simply that Reapers are the most obvious and noticeable.
(Although, this doesn't mean all Litanists are evil or something. Just a scary amount of them.)
