On the interspecies front, the most ridiculous thing I've seen in sci fi is the fact that Major Kira hesitated for even a second when offered the opportunity to have sex with someone who can control the exact size and shape of his stuff. I guess the writers wanted to hold onto racism for a few more weeks. "But she's a former terrorist. She has to fall in love with the cute Arab doctor."
But I have to wonder why interspecies breeding is a space opera trope at all. Who was the person who started that trope? Was there a nerdy sci fi writer somewhere who said, "I would love to travel to outer space, and by some bizarre quirk of parallel evolution meet a species of aliens where the females at least look mostly like attractive humans, except for maybe skin pigmentation or pointy ears or some forehead or nose ridges. And then I could have sex with one of the hot alien women, and... accidentally knock her up." It's that last part that I don't see ever happening.
This is a really old trope too. In an old episode of Rocky Jones, Space Ranger, upon landing on an alien planet, the boy sidekick goes off to play with the princess. Although they are just children and their relationship is very innocent, she is very pretty. One wonders what will happen as they grow up. She is apparently a recurring character but I've only ever seen the one episode.