Same here. Even looking at the art gallery of the
Book of Vile Furries (BOED) should tip one off about that book.
And here is the Book of Vile Darkness art Gallery
I couldn't find the trope name looking through TV tropes, but there is this reoccurring theme that often shows up in stories and in fantasy in particular where Good is Also Evil. The basic idea is that any extremist for good is also evil. That is, as a person becomes more zealously good, there comes a point where they cease being more caring, more honest, more benevolent and start becoming more cruel, more hypocritical, and eventually malevolent. Anyone that appears good inevitably falls or turns out to have been the villain all along.
You might recognize this as the seemingly strange alignment of True Neutral in the original 1e AD&D, where right action was defined as making sure none of the alignments actually won because extreme goodness would be just as horrible as extreme evil. D&D has always leaned really heavily on the trope. It also shows up as Pholtus the 'good' deity of cruelty, hypocrisy, arrogance, and lack of compassion in Greyhawk, and its not accidental that Pholtus and the description of True Neutral came from the same source. But it also shows up in 'Chronicles of the Dragonlance' when it is explained by a 'good' deity, that the gods inflicted the cataclysm on Kyrnn not because the people had become hypocritical, cruel, banal, unmerciful, self-righteous and so forth (and therefore, no longer actually good), but because they really were 'more good' and even the 'most good' people had ever been and this most goodness was actually responsible for the aforementioned traits. In other words, good and evil are basically the same thing in their extremes, and things have to be kept in balance - as 'wise' good people know. And it shows up in pretty much every Paladin every presented in any detail in D&D history, where Paladins are at best pompous jerks or weak naïve victims, and fallen Paladins outnumber righteous ones by a considerable degree. The story arc of the Paladin in Neverwinter Nights was so ordinary as to be the conventional depiction of Paladins in D&D. And while Order of the Stick typically treats alignment with a lot more depth and thoughtfulness than TSR/WotC published works, Miko is pretty much full on in the middle of this trope. The heroic and sympathetic portrayal of O-Chul is unusual in D&D media for giving any indication that there are Paladins you might like to know, and that such types aren't wholly outside the norm.
When I started glancing through Book of Exalted Deeds, I really felt like I was reading the work of someone that really believed the 'more good is the same as more evil' and was deeply uncomfortable with the subject matter or with portraying good in a sympathetic manner and not as some more pathetic less clear eyed version of evil, or conversely that evil was just really misunderstood. The BoVD wasn't exactly good source material for how vile evil and darkness actually can be, but at least the writer wasn't writing from a conflicted perspective.
