I have found no standard English (that is, non-slang) word to use in the sentence, “He went home to _____ his wife.”
Words like “bang”, “screw”, and “nail” can be used on TV but are slang or euphemisms, not standard English. “Have sexual intercourse with” and “have sex with” are phrases, not a single word. “Fornicate” is standard but implies sex outside of marriage and can’t be used as a transitive verb.
Is there a standard English equivalent word, not phrase? If not, why not?
I think you ignoring phrases is the trouble. Lots of things cannot be expressed in just one word. If it was the case that everything could be said in one word, then we’d have a really enormous vocabulary, and every sentence would be really short.
So yes, “have sex with” is what you’re going to be stuck with. It just so happens that the 3 words you chose as examples happen to have one-word “proper” equivalents. And fuck doesn’t. That’s language for you.
Why not? You might be more familiar with "to copulate with his wife, but I think “to copulate his wife” is still proper English, as is “to know his wife”.
However, the sentence “He went home to copulate’” is perfectly correct. The problem (which is not really a problem) only arises if you insist on specifying the partner involved in the act. You might as well say there is no proper English word for “talk” since you have to say “talk with” if you specify another person involved.
I remember in fourth grade, history class came after sex ed. This would have no bearing normally, but when the poor lad assigned to read that day’s lesson said: “Under Alexander the Great, intercourse among the nations was the greatest ever”, the class laughed and he turned beet red.
I’ve thought for a while that there ought to be an adjective, analogous to “hungry,” “thirsty,” “sleepy,” or “horny,” for the feeling of needing to go to the bathroom.