Both authors assume that what we call "intelligence" and "sentience" is deeply influenced by the environment our species evolved in (plus a billion happenstance

Both authors assume that what we call "intelligence" and "sentience" is deeply influenced by the environment our species evolved in (plus a billion happenstances) and that therefore any dream of meaningful communication with extraterrestrials is a naive dream. Now, we don't know if they're right because, as you pointed out, we never met actual aliens. But that doesn't change the fact that their assumptions is based on actual science. Klingon mating rituals, on the other hand, are not.