I’m gonna have to argue the anti-dark titles from a certain point of view. Watch out: Narg is gonna ramble now.
The reason why a lot of hentai is the dark stuff, is because the pure stuff gets non-hentai conversions. For example you have general market anime for Da Capo, To Heart, Comic Party, Tsukihime, etc.
Hardcore series like Midnight Sleazy Train or Black Bible use the dark sex as an integrated part of the story. While a series like Tsukihime and FATE has sex as a factor in the plot, it isn’t so entrenched that it can’t be removed without drastically altering the premise. As an example, MinDeaD BlooD or Gore Screaming Show loses a lot of itself when dropping sex - even if the said action takes place “off camera” or whatnot. Crazy as it sounds, the violent sex is that important.
Since the “pure hearted” stuff is released by groups like ADV and Funimation, that leaves companies like Kitty Media to cater towards the niche group that prefers the “evil hearted” stuff.
From the Japanese producer prospective: why release a hentai OVA of To Heart 2, when the money can be spent to mass market an “all ages” version that will make more $$$ for the investors? Thus you won’t get a hentai anime of To Heart 2. On the other hand, why make a non-hentai OVA of Midnight Sleazy Train 2, when the targeted market for the game got it for the hentai - not the story. While it does have a good plot, the plot itself was just icing: the meat and potatoes was the train molestation. Hence you’re not going to get a non-hentai version, because it would alienate the original target base.
Thus I see nothing wrong with Kitty Media releasing the dark stuff over the pure hearted, simply because it’s the dark stuff that sold best. However, you can’t really blame the Western license holders of the anime such as Da Capo, To Heart, and so forth - for not releasing the b-games for them, because they don’t want to deal with hentai. Had there not been a non-hentai version of the titles, they wouldn’t have even bothered. Not only this, but the non-adult games were typically released on Playstation 2: and SONY of America ruthlessly crushes 2D game releases for that system (and the PS3 for that matter).