How many times have you tuned in an episode of Star Trek and seen someone “breeding” with another species? Too many to count. What’s worse is Star Trek says different species evolved in isolation can breed and have fertile young. If two organisms can breed and have fertile young, they are by definition members of the same species. Star Trek: The Next Generation at least tried to address this with an episode that claimed all humanoids are derived from a parent species of humanoids. I’ve seen other shows do it without thinking too much about it. The only counter examples I know of come from the Star Trek novels and Babylon 5. I read the novelization of Star Trek V: The Final Frontier before seeing the movie. The novelization mentioned that Spock, born of a Vulcan father and Human mother, was conceived with a lot of technology. The movie made no reference to this, but it wasn’t really important. This isn’t surprising since the Star Trek novels have always said interspecies breeding isn’t possible without lots of medical intervention.
Babylon 5 understood the concept of different species breeding, but in order to get two species to breed, used a magic machine (being assembled by Delenn in “Chrysalis”) to half convert Delenn into a human-Minbari hybrid.