When I say "banal evil" I just mean the same kind of evil humanity has had to contend with for all of our history: slavery and racism, of course, but also destructive greed and non-consensual prostitution, organized crime and official corruption. Those things usually exist in the world, but I don't dwell on them or they serve as an in-road to more operatic evil. For example, if raiders are taking slaves and the PCs go to stop them, the trail never just ends with slavers: the victims are to be turned into monsters under the control of some would be demon lord, or whatever.
I am ambivalent about including stuff like brothels or dog fighting or abused labor or other "minor evils." They can be background flavor, I guess, but if they get more than a passing mention when I am trying to paint a picture of how nasty the big vile city is it would be a surprise to even me. Unless I just finished a Black Company book or something and am in the mood to get vile. that happens sometimes.
I honestly don't know where to start with this post. We are putting continuous rape of men and women for profit on the same level as overlogging a forest because the lumber baron gave the mayor a sack of gold.
Maybe I'm the weird one, but I don't tend to make vile big cities where slavery and rape are common, where diseased beggars die in the streets and gangs shank people for fun. I can't imagine wanting to make a city like that. Sure, I might have a gang or two run by a mob boss, but he's more into smuggling, illegal pit fights, and blackmail. Things that are crime, but aren't going to involve dog fighting or prostitution. Heck, I stitch together a few different eras of humanity including the modern day and if I have Pleasure Houses, they are places that are legal, well-run, with medical care, that are full of willing people who like their jobs. I'm sure that has never all happened in one place in human society, but we've had parts of it, and we also don't have a lot of other things in a fantasy setting. Why can't I make part of that setting be that things are... not naughty word?
Like, people keep saying that we have all these historical periods, and we should make sure to take slavery from Rome and serfdom from Europe and this from there and that from over here... why can't I decide to take acceptance of Transgendered people from Native American traditions, a culture of bathing and cleanliness from the Saxons I believe it was, maybe some gender equality norms from African Tribes. I'm not saying have no conflict, no simple evils like conmen or criminals, but... I don't know.
Not directed at anyone in particular, but it feels like the more I read this thread, the more people seem to be of the opinion that if you aren't including some of the most vile acts of human depravity in your setting, you aren't really making a good DnD setting. And that just feels so viscerally wrong to me.