At least, thanks to ENT, there's an explaination for Spock. It probably required a lot of medical work to create him. Even Vulcan blood chemistry is different than Earths, so it wasn't Sarek looking shocked in the morning and telling Amanda "oh shit, I thought you said you had an IUD. You meant Interstellar University Degree.. right.. well" .
Various writers seem to think that Klingons are at least somewhat human, or avian, or lizard, and now generously blessed in the two-of-everything department. How they produce offspring with both humans and reptiles and the porcine Tellarites is difficult to understand.
Betazoids seem a little closer to humans. Anyway
It being often used canonically doesn't make it less silly.