I'm glad my rant could be helpful. LOL. I was just feeling frustrated.
Quality of writing always impacts how you view a scene, definitely, and I do think that it is often thrown in for appeal and not purpose. Which is great for that particular audience, and a turn off for others. But we reveal a lot about ourselves when we're naked and vulnerable. Obviously it has to be done appropriately, but I would say that about anything we write.
If your story is about mystery and you think details of MCs having sex doesn't add or interrupts the flow, then certainly don't put it in or just infer it happened. I do that with other novels, and leave the emotions and reactions for before and after. But if it is a step in the relationship and is used to further character understanding and development, I think it's natural to include it. Go for it! It's also challenging to write as an author, giving you another layer to storytelling.
And sex doesn't equal porn. Porn equals porn. Why all sexual content gets lumped together into smut once it hits the media is beyond me. And even "smut" can be done really well and further characters and story. The definition of smut is really just based on someone's comfort level.
Ah, I need to step out. I'm feeling surprisingly passionate in defending sex in novels.