Sometimes I hate lemon scenes

[Nate Hunter]

And "we won't get laid easily", while very proper grammar, is a bit stupid of a statement to make. If we are in a peaceful and happy place, that indicates a lack of conflict. A lack of conflict indicates an widespread acceptance and tolerance, which means that we will have less cause to judge our mates, as if we don't enjoy their performance, company, or whatever, we can simply tell them we'd like to go our separate ways in peace, without fear of reprisal about it. Therefore it would be easier to "get laid" because we don't fear anger, jealousy, or any other risks.

Judging one's mate is an instinct, because you want to mate with the best genes you can find.

Also, I'm trying to think if a very good idea for creating the sex scene breaks the theme. On the one hand, it makes the conflict far more substantial and real, but would make the entire story and theme darker.

But sex among humans is more than just procreation. If your utopic world has sex only for procreation, then you throw your entire concept out of the window (sex for procreation and preserving genes would not be likely to occur between different and presumably incompatible species), while still having it for pleasure means that you could mate with anyone without fear of an unwanted child, because you could either control, or easily prevent unwanted, pregnancy. Judging a mate is an instinct, but a mate is only one you intend to procreate with.