This is hardly a porn game. You have to play for several hours before seeing anything and often times, the sex scenes add to the character and are quite tame (Minthara's is the most explicit, everyone else's though could be considered PG-13 if it didn't have nudity).
Sex is used to enhance the intimacy of relationships or to show the callousness in characters and I believe BG3 did that pretty well.
Its just like with Game of Thrones. That show has sex all over the place. But what it doesn't do is devolve into straight up erotica. Sex for those characters is used as a weapon, as an intimate moment, to push the story forward, to connect with characters which is exactly what I think BG3 does with it too.
Now, I do believe Halsin was just there for gratification, that is pretty obvious. But Astarion's sex scenes make clear aspects of his character and are somewhat crucial to get to know him on a deeper level since sex and control are such poignant parts of his character, SH's is a big step for her character and being vulnerable with you which is something she's never let herself feel, Karlach's also gives her a softer-ish side and it helps me relate to her, Gale's is just...fascinating to me and makes him fascinating in turn, Minthara's is all about control and dominance and it sets the stage for her if you fully romance her and breaks down her vulnerabilities to the point that she admits her regrets at treating you this way once real feelings set in. I could go on.
The fact is, in real life, sex happens all the time. On the first date, the first sentence, a fling at a party etc. And this game tried to be sure the sex scenes served a purpose for their characters (except Halsin) and I believe they've done that successfully.
