tl;dr: It's all about the presentation, baby!
I wouldn't really describe TLS as a 'porn game' per se, but I do agree that it's got a lot more sexual content than most people would be comfortable with, especially when it comes to the heavily frontloaded earlier chapters. The type of sexual content might also be a turn-off for most people. I'm not ragging on other people here, mind you- I can certainly understand people being uncomfortable with the themes of consent (and its lack), for example. Hell, I'm not really comfortable with incest themes at certain points in the story, but that's just a me thing.
Honestly, I think the best way of presenting TLS would be in the form of a written Let's Play or summat of the sort (which I am actually planning to do if/when the game is finished, so I have more context on things), where the player and the audience can discuss the ideas and themes presented in the game between updates. After all, one thing that I think is easy to see from the finished-so-far product is how Sierra herself has evolved as a writer (not to mention scripter), and bringing people along that journey in a safe, guided environment might be the best way of sharing your enjoyment of the game and its themes.
That said, I think it might be an easier sell than most might think, especially if it's bolstered by an LP. I know it's easy to think that people would be turned off by the sexual content in the game, and that might have been so back in the late 90's and early 00's, when Concerned Parents' Groups™ and their ilk were protesting against everything that The Kids(also ™) liked. Now though? We have mainstream games like The Witcher, Dragon Age, Mass Effect and Cyberpunk showing at least some degree of nudity and having some kind of sexual content, while in greater culture there are people all over who are fighting for the rights of marginalized groups like sex workers.
Really, the only truly objectionable sexual content (at least, in my opinion) in TLS is the stuff where informed consent is overidden (e.g. whoring Qum in Stineford, that one 'pet' of the Fucklord- holy shit everything about that guy infuriates me, not least because I was him 20+ years ago, aaargh). Which again, is why it would be important that someone who knows the game be there to act as a curator or guide and provide context, as opposed to chucking some poor newbies into the deep and and telling them "All right there buddy, enjoy the rapey bits! I know I did!". Sure, that may not be what you're telling them, but without some kind of the aforementioned context, that's what your victims will remember you saying.