If AVG galgames are foremost about the story, the question is equivalent to “is it possible to have dark stories with ero” or even better, “without rape”. I think anyone who read a lot would answer a resounding “YES!” to such a question.
Here’s probably a better way of stating what I was getting at: a dark game focuses on rape for the sexual gratification of the player (whether the protagonist is involved or not), which is why it’s rather ero(game) specific (in my mind). Fate/Stay Night has a dark story at times, but there’s only one scene I can think of (Saber being tortured by Caster) where it seemed like the scene was trying to get a sexual rise out of the player through brutality and violence.
I’m guilty of it too, but the problem is that classifying eroge as “Light” and “Dark” is too general. It’s like labeling all commercial road vehicles are “Trucks” and “Cars”. You can do it, but there’s so many classifications inside of that: buses, semi, pickup, SUV, limo, etc.
Using the old system of Shakespeare: all Dark eroge are Tragedies, and all Light are eroge Comedies.
Well, for my part, it’s rather silly to create yet another definition to “dark”, to apply only to galgames. If you say someone that a novel, a movie, an anime, a comics is ‘dark’, most people would get it already. There’s no reason to give it any other meaning (e.g. “contains rape”) when applied to galgames.
There’s no rape in Tennoinai, but I doubt anyone would qualify it as being but ‘dark’.
If speaking about erogames where story is an important element, people do classify stories as being ‘light’ or ‘dark’. Why absolutely want to turn erogames into a peculiar case? If I tell you that Miller’s Batman stories are rather dark, is that “too general” to describe them? I personally don’t think so.
…and, no, they don’t have rapes narrated inside. 
Even movies have “sub-categories” though… comedies, action, thrillers, horrors, sci-fi, etc. Then you have things like “dark comedies” and “light comedies” to differentiate them further.
The Godfather trilogy and The Chronicles of Riddick series are both dark movies… but totally different beasts too. One is a Mafia film and the other is a dystopia sci-fi. Just labeling them “dark” is okay if you’re generalizing… but if someone asks if I want to see a dark movie, I usually want to know what kind of dark movie it is. I don’t wanna see a dark chick flick, but I’ll jump aboard for a dark action movie.
I think eroge is about the same in that regard.
But erogames do as well. I don’t think the point was to only use ‘light/dark’ to qualify them, but merely how to apply those qualifiers to them. To what I think it’s silly to want to give ‘light/dark’ a connotation/meaning when applied to erogames different than when applied to any other material where the story has a place.
Ah… I see what you’re saying now.
I suppose the connotation of “Light” and “Dark” with western erogers, is because in the early 2000’s of English eroge, the more “popular” titles were either [color=blue]happy-happy go-lucky romances[/color] (oh so kawaii!) or [color=red]brutal violent rapefest paradises[/color] (yuck! yuck! yuck!).
Thus light and dark. Since then market has expanded somewhat, and more about Japan’s massive library of titles that we’ll never see in English have become known, but the monikers still stuck.
Got that right. The way it ruined what had been an interesting IP by ripping out everything that made Pitch Black awesome is one of the dark days of cinema, indeed …
Well also, defining light and dark in such a way presents a pretty sharp divide between two target audiences. When defined this way, fans of “light” eroge tend to avoid “dark” eroge, and vice versa. In that regard, it’s a useful black-and-white definition for helping eroge fans find what they want. However, if you define light and dark in the usual non-eroge way, you gain consistency–but now your parameter is not only much more subjective, it’s so broad that it’s no longer as useful a predictor of like/dislike (a fan of a “dark” game like Nocturnal Illusion is still likely to like a “light” game like Seasons of the Sakura, and vice versa). So then it just becomes a vague descriptive term that isn’t terribly useful either for description or prediction of like/dislike, at least by itself.
I just remembered a few games i think are dark. Chaos;Head (Delusions, isolation, thriller, psychological, non-ero), and Saya no Uta (Everything looks like a dismembered person). Also Tsukhime (Pretty strong story), and Higurashi no naku koro ni (Horror. Has an anime, a PS2 remake, and a scary as hell manga. Only the first story was translated though.)