To me, what it makes him, is a conflicted person, who doesn't magically get over that conflict instantaneously. There's a world view that what he's feeling is wrong, which he has accepted for most of his life as true. There's the fact that for much of his life he has devoted himself to protecting these girls from people who wanted to do very similar things to what he's doing with them right now. Is it different because it's what the girls want? Absolutely, yes, but that doesn't magically make the guilt go away, or the sense of hypocrisy.
Is this a fantasy game, and is it valid to write it in a way where he doesn't have this conflict? Absolutely it is, and there are tons of fun and good games that do things that way. However, *not* doing things that way gives this game unique aspects which I, and several other people do enjoy. I enjoy that it feels like Becca and the others are corrupting Frank, and that's not possible without the inner conflict that you dislike. I feel like it's more true to a situation where someone's daughters suddenly decided to try to seduce them than what we normally see in these types of games, and while that's not necessary, I find it refreshingly different personally.
This is not to say that your viewpoint isn't valid. You're free to dislike it, and to state that dislike in this public forum. I only respond, because it's important for people like the developer to see that there are those with an equally valid viewpoint on the side of how they are currently writing the story so that they can make an informed decision about whether to continue writing it that way.
