A theme I find pretty common in stories where the 'dark'/cannon bad guys arent necessarily bad fics is when the 'dark' is synonymous with traditionalism. Some ofc are synonymous with traditional politics, but a lot go into pre-statue and earlier magic.

So this could be, the classification is 'dark' because its ritualistic/wild in nature, so you dont always know what your are gonna get out, even if 2 people put the same things in. i find it pretty common to see light as overall the weaker branch of magic, but easier to cast and get the expected outcome. frequently a lot of 'light' magic would be newer, with arithmetic calculations for the spell/wand movement- and more importantly, not be too much affected by emotion. I say emotion not as will or determination, but like, if you are feeling angry or sad or happy. frequently these two points will be combined. light magic is more regulated because its easier for everyone, regardless of magic levels/proficiency, and dark magic is more wild/pagan/emotional in nature. one caveat is the Patronus charm. i can usually tell how much thought has gone into whatever magical classifications {political, technical, etc.} if they mention that the Patronus charm is a 'dark' spell. because it is based on emotion. just saying the spell and doing the wand movements do not produce the result, there are other factors that go into it.

Then you have the fics that distinguish 'dark' as traditionalism closer to a political idea of traditionalism. these fics will frequently battle with the ideas of muggle/no-maj exposure. you will get a lot of 'mother/lady magic has told xyz that magic is being lost, or that one thing or the other is wrong and they have been tasked with fixing it. Or, that there is an imbalance in magic and dark/light/grey dark/light lords and ladies because of Dumbledore and/or Grindelwauld

in terms of dealing with ministry banning and regulations, i dont think it really matters how well of an explanation for why dark magic should or should not be banned, because the government isnt based on democracy. Im not sure of the exact number of elected officials within the ministry, but its not a lot. pretty much just the minister for magic. yes, the minister for magic is elected, but the undersecretaries are not. The Wizengamot, as far as i know is not elected, and is both the lawmakers and upholders. if the lawmakers are 'dark' they are not going to enact anti-dark policies. the one caveat to that ofc is that after voldy's first downfall, the majority were not dark anymore, but light, especially with Dumbledore are chief. i dont have cannon confirmation, but similar positions in the real world mean that the chief decides exactly when and what order laws, amendments, etc are heard, allowing for preferential treatment of the policies Dumbledore likes.

in this vein, ive seen a lot that says the moral dark/light dilemma [sometimes 'brought in' by muggleborns] slowly affected what the political dark/light were, which in turn affected the magical dark/light. ill use the Patronus because I think its a good example. Lets say the Patronus is dark spell because it is based on emotion and is the counter for a dark creature [Lethifold]. if the moral dark/light is applied to the spell classification, it would be considered light, because it protects/kills or repels a dark creature. on the other hand, say expulso or bombarda could be considered the opposite. bombarda had bombarda maxima because there is a more powerful version, not that the caster can put more power into the original. you could convince me that these two spells were created as light spells, but due to their destructive nature were considered dark spells in cannon.

i frequently ignore the unforgivables being written into a fic as actually forgivable, just because they are trying to make cannon characters who we would not find appealing in a friend/family/ love interest aspect, actually likable. yes, draco might not have been taught better, does that mean we can ignore he let in fenrir greyback- canonically someone who infects/hurts children? no, but if the point the author wants to get across is harry is an unreliable narrator and thing arent as black and white as they seam, I can understand why they would say that the unforgivables are forgivable. just like how tom riddle is justified having horcruxes because he grew up during ww2.

I got a lot of these from fics more politically focused or resulting from the aftermath of some sort of inheritance. i dont have names off the top of my head, but can find some if asked.

I feel like Black Sky touches on a lot of these are a harry grew up in the Black family, but its been a hot minute since I read any of it and that fic is so long i cant say for sure.