Man I lost the first version of this reply and this second one isn't quite as good (and the first half is not really a reply to OP). Anyway:
The topic of portayal of sex has been subject to a lot of discussion, speculation, prejudice and expectations ever since this project was created. Though there are forces pulling to different directions, all of us have had to pick their stance a long ago.
Generally speaking, I think that KS is not trying to make a statement about disability. Sure, the angle we chose is that disability does not define a person, and we think a lot about how we portray disability, but there is no moral in KS, apart from a subjective one a reader might find.
While the fact is that there are things that are inappropriate for youngsters, there is a bigger issue behind it. Does the inclusion of sex, possibly explicit, possibly even something one might call "porn", into something that might be called a "serious" work devalue the latter? While this depends on a lot of factors, I think the answer is more likely to be "yes" than "no". It's simply a part of a more universal issue. Just like a heartwrenching drama might be ruined by an inappropriate slapstick comedy moment, a work can be ruined by an inappropriate sex scene (and it's harder to not make sex scene feel inappropriate). A concrete example that comes into mind is Saya no Uta, a decent horror visual novel that was completely ruined for me by the explicit porn and rape scenes it had. Notable is that the fact it had sex or even rape didn't spoil it, the way those scenes were handled did. From this I conjecture that it would've been possible to display those events in a way that would've felt appropriate to me, and to extend, appropriate to most mature audiences. The leagues of movies that have sex scenes support this observation. Speaking of movies, another example I think about often when I think about portrayal of sex in visual media is the lovemaking scene in Zack Snyder's movie 300. It's basically as close to porn as you can get in a Hollywood movie, but I don't think it necessarily devalues the rest of the movie for me. I admit though, considering how often I wonder about that scene it very well might've ruined the entire movie for me. Still, it seems that there is some invisible, intangible line where "sex" turns into "porn" (here I use "sex" as shorthand for acceptable portrayal of sex and "porn" as shorthand for unacceptable or distracting, devaluing portrayal). If we go to Katawa Shoujo from here I'd say that the sex (not porn!) scenes that I made for KS do not devalue it for me, because I took EXTREME care that the scenes and their visualization would not cross the line of acceptability for me. I expect that others disagree, after all this kind of thing is awfully subjective. My developer colleagues have different opinions as well, and they have made their points of view come alive in the parts of the game they made. However, my stance is that just like I try to portray disability in a humane and compassionate way, so do I try to portray sex and sexuality too. I do encourage you to give me a chance to show it.
There are some things here that I can't talk about now, when the game is not released. After everyone has had a chance to read the sex scenes and see the stylistic choices, I might write something about the thoughtwork that has gone into making them.
As for younger audiences, the problem is a bit difficult. That KS appeals to you (and you are not the first) as an instrument to instruct or communicate acceptance of disability speaks to me of the sad, sad state of portrayal of disability in our culture. And for once, I'm not being self-deprecating. It's evident that KS, or at least Act 1, somehow managed to do at least something right with the topic, however it is greatly lacking in its treatment of the themes, because it's really about something else. To create a haphazard analogue with a reference already used before, it's like using the movie 300 to communicate appreciation of ancient Greek history. While the movie might've gotten some things done right and because it's less boring than a history text book, it feels appealing for the purpose. It is quite possible that someone, having seen the movie, is inspired to read about the real history of the city state of Sparta, maybe even all of Greece, but that's not what the movie is for. Similar line of thought goes for KS. That aside, I do understand that the inclusion of sex closes the door for KS from having parents recommend it to children, teachers to students or even just simply anyone to their friends. Still, with the exception of the sex scene toggle, KS is made with no considerations for the reader's sensibilities, be they due to young age, cultural background or moral norm set. That is because we can't decide what we should conform with and what not. To illuminate the issue further, let's say we made a version with the sex scenes completely removed. Now, some parents might feel concerned that the swearwords KS has cross the line for their kids, so we have to make a version with no sex scenes and no cussing. Enter the people who are offended by Kenji's rampant misogyny and antifeminism. So, we have to make a version with... See? Sex is the obvious big one and we made that toggle, but that is where it ends (unless we decide otherwise). KS comes as it is, if you can't handle some of the content we can't bend backwards to make it palatable especially for you. While it's possible that sex is the only issue that is big enough that people start drawing lines, I'm not at the moment inclined to go down that path. Further, even if we made a "clean" version of the game, it would only take one Google search for an industrious youngster to find out that they are getting a censored version from their parent/teacher/whoever.
From your choice of words, especially "it could be so much more", I interpret that this aspect strongly devalues KS for you, and I think that is very unfortunate. Someone thinking that a work I made is good is wonderful, but to consider recommending it to another person is a great honor for me, and I feel sorry that KS outgrew for you the box it is in. Similarly, the prejudices surrounding the visual novel medium (and to some extent the entire otaku subculture) close some doors from KS. I guess, in a world devoid of compassion for disabled people, maybe KS could be more than a simple love story, a story that speaks of humanity and the world of disabled, of the grief of otherness and exclusion. But a bit idealistically (you can laugh), I object: KS is exactly what it is, nothing more. It is the world that should be more openminded and accepting.
I'm gonna put this on blog. Why can't every thread OP be like this?
<Aura> would you squeeze a warm PVC bottle between your thighs and call it "manaka-chan"
<Suriko> I would do it if it wouldn't be so hard to explain to my parents