First, I acknowledge you pointing out that fiction and reality are different things (especially where porn and/or videogames are concerned), and I won't assume your perspective on real people is the same as your perspective on the girls in the game. I'm glad you brought that up. It's always good to remember. Sorry if that comparison seemed a bit too cranky. There's just not a lot else to use as a basis of comparison. Also, it's nice to have more involved discussion than "NTR sucks!" "No, you suck!"
I couldn't remember the details of all the Bad Ends over the course of the game, so I just went and re-watched the Hunter scene for Ch.10 to use as an example. We don't know exactly how much influence the drugs in the food and wherever else may be influencing them or at what pace that may have built up, only that it is an effect which should benefit Hunter and Sterling equally. Even Sterling himself admitted that that is a concern to him, so, no denying that is a factor.
At this point, Sterling has already been building these relationships for some time, where as Hunter is still basically at zero points. Meanwhile, the effects of the drugs have ramped up in the last couple of updates.
Unfortunately, even in real life, there is some amount of questionable risk involved with having sex when people have been drinking. Assuming a relationship already exists or there is at least an agreed upon expectation of sex, most people wouldn't take issue with doing some drinking before hand. However, the same amount of alcohol could be exploited by someone trying to seduce a person would might otherwise not have sex. That's an awkward issue that creates arguments that go way beyond our debating a porn game.
My point is, Sterling having sex with the girls while they're under the influence of these drugs (or additional alcohol) is different from Hunter taking advantage of the drugs, due to the time already put in to the relationships. It's an uncertain factor, but Sterling is trying to be aware of that, typically stops when told to stop, and even tries to stop the girls if they go after him when he feels things are moving too quickly. He may try to make his case to them, but he ultimately waits until he feels confident that they are making the decision themselves. By comparison, Hunter will fast-talk, nag, manipulate, grope, and do whatever is necessary to push them into sex when given the opportunity.
SPOILERS AND GRAPHIC NTR DISCUSSION FROM CHAPTER 10 AHEAD
In the example of Hunter's Bad End in Ch.10, by the time Hunter gets there, Ophelia and Aliza are excitedly anticipating sex with Sterling and have already been drinking wine (which in the canon path is implied to have been provided secretly by Hunter and has further drugs in it).
He starts by garnering sympathy faking an injury, draws attention to his scars, and tricks Ophelia into "examining" his penis and balls hands-on and up-close, even encouraging her to "take a deep breath" (this may or may not align with the idea from What If 6 that he puts some kind of aphrodisiac musk scent on himself). He then brings up the fact that she has already crossed some incest lines with Sterling, which both nukes that hurdle using Sterling's efforts and brings up the topic of sex while she's already holding his penis. From there, he continues to badger and manipulate her, refusing to take no for an answer, until he's able to get as far as taunting her by rubbing his penis on her vagina while preying on her pre-aroused state.
These are all things that Sterling would never do or plan. This is why Hunter can get them faster than Sterling, and while Sterling does benefit from the tainted wine in the canon path, he isn't even aware of where they got it until afterward, so he can't really be blamed for that.
