I was musing about obscenities both English and in other languages, and thought that most obscenities involve either:
–suggestions one’s mother is promiscuous
–suggestions that one is a homosexual
–urination/defacation
So are there any languages that don’t use these kind of obscenities? And for that matter, why are insults about one’s mother more common than ones about your father?
I suppose the mother is more common that the father because many people are more sentimental about their mother than their father.
But I’d think that insults about oneself are more common than any other: “Fuck you!” “Screw you!”
Also, beyond the sexual and excretory areas that you listed, consider also the more personal curses: “Idiot!” “Asshole!”
Don’t forget religious curses: “Damn you!” It is my observation that people aren’t praying as much as they did 50 or 100 years ago, but the cursing is still going strong.
In short, I think the premise of the question might be in error.
Hmmm… I just noticed that although the title of the OP refers to “insults/obscenities”, the question itself mentions obscenities thrice, and insults not at all. That could be very telling right there.
In any case, obscenities are valued for their ability to shock, and in previous generations general curses were in that category too. But nowadays, not much is taboo beyond the stuff you mentioned. For example, insulting one’s father is going to be pretty useless in a culture where your victim might not even know who his father was, compared to knowing one’s mother.
The standard insult “Bastard” implies one without a father.
Often used with modifiers so “Stupid Bastard”, F**king Bastard", “Tight Bastard” (implying parsimony) and so on.
TCMF-2L
This was a thing when they did Deadwood, the HBO TV series.
They wanted genuine salty language from back then, rough and raw Wild West frontiersmen insults and obscenities. But when they did the research, they found that the most shocking stuff back then was blasphemous, i.e. denying the trinity or some such, which doesn’t really shock us modern folk.
So they reverted back to what is more shocking today: “Motherfucker,” “cocksucker,” and all the rest of it.
“Oh that Wyatt Earp feller’? Pardon my French, but I hear he’s a dyed-in-the-wool Patripassian, that one. [audible gasps] Apologies to the ladies present, but it must be said: The man even disagrees with Melanchthon on the concept of Synergism! [swooning left and right] Even believes in the Peshitta Primacy, fer Chrissakes! [riot ensues]”
To call a woman a bitch in the United States is a supreme insult to a woman here and will be responded to with a full out nuclear attack. Call a Japanese woman a bitch and she will just give a strange look (unless she has spent a lot of time in the states). I’ve been told by the Japanese that if you truly want to insult a woman you just need to refer to her a big cow. Kind of works in any language. 
You have a father everyone does. The insult is that your mother was promiscuous as stated by the OP.
The OP may be interested in reading *The Anatomy of Swearing *by Ashley Montague. History, meaning, examples in many languages. Very scholarly…and entertaining! Imagine getting a research grant to study cursing.
You’re correct in that there are “categories” of cursing - anatomical, scatological, sexual, compound terms. According to Montague, effective cursing is an art form.
There was a journal you may be interested in:
It can also mean that your biological father was a low-life prick who refused to do right by your mother.
I think the B-word is losing it’s power to offend. You can easily imagine a woman going, “Tee-hee, I’m such a bitch, aren’t I?”
But the c-word… that still has power.
Depends on how you say it. You must be doing it wrong. It needs to come from low in you gut with proper diaphram control to be effective. Practice. . . . Practice . . . Practice is the key.
Your mother was a hamster and your father smelt of elderberries!
Your mother could have been raped rather than being promiscuous. Some will argue that makes your mother violated and less worthy. Others would suggest it is a slur on the rapist.
Clearly we disagree but in my experience calling someone ‘a bastard’ insults the individual so called, not specifically their mother. Although you can get meta and say the insult derives from their mother’s (real or socially contrived) failings.
Otherwise we wouldn’t need the insult ‘son of a whore’ would we? 
TCMF-2F
In Spanish, the most severe insults you can give to a man are to indicate that he’s a cuckold, that is, that his wife or lover has been unfaithful to him.
Insults to one’s mother are pretty high up there too.
This reminds me of the wonderful film Stand by Me. The Writer: [voiceover] “Finding new and preferably disgusting ways to degrade a friend’s mother was always held in high regard.”
I had always thought historically that blasphemy was the traditional way northern Europeans swore like the English ‘zounds’ (God’s wounds) and the French sacre bleu (reference to Mary), etc. Spanish insulted your heritage (tu madre), Arabs your person (may 1000 fleas…), Americans bodily functions and you. Where I got this idea I don’t know. Pulp historical novels?
I did a cursory (ha ha) googling and didn’t find a thing to back me up. I do feel strongly that modern cursing is WAY less interesting and colorful. Great Caesar’s ghost! Jumping Jehosaphat! People really use about 3 exclamations over and over.
The homosexuality category is really just a subset of a larger category IMO. That category is sexual deviation from normal/right/proper sexual behavior as defined by cultural norm. Homosexuality is just a popular one under the category. There’s not a simple one word noun for a lot of those other bits of fun…er deviations.
Nothing beats me cago en la leche que te pario, i.e. “I shit in the milk which fed you,” meaning the mother’s milk the guy suckled as a babe. Can’t think of an insult more truly vile and nasty than that.
Thai may be an exception to OP’s thesis. I see I mentioned the most common Thai obscenities in an earlier thread on this topic.
Some Thai cussing involves pronouns and other simple parts of speech. I met my bride’s father the day before our wedding and he referred to me using the pronoun “it.” That might have been a deal-breaker if I’d learned Thai only by reading Bernard Trink’s column in the Bangkok Post. :smack: Fortunately I was already familiar with some differences between rural diction and Bangkok middle-class diction. And indeed my father-in-law used the same “it” pronoun to refer to his adult children.