The movie ratings system is a mess, these days.
In 1968, it was a vast improvement over the "Hays Code" (which was itself a vast improvement over the absolute freedom, untempered by any sense of responsibility, that had preceded it), but it was far from perfect.
The thing to remember is that it was
never intended to be anything other than an indication of suitability for children. (And the one absolute, non-negotiable requirement for a seat on the ratings board is that one
must be a parent.) And it was intended to say
as little as possible about the content (presumably to avoid spoilers). And it was intended to give moviemakers enough artistic freedom to differentiate their product from television (which, at the time, had to be, as somebody who wrote an early Star Trek nonfiction book [David Gerrold?] put it, "as inoffensive as vanilla pudding").
As originally conceived, it was a system of G (General audiences), M (Mature subject matter), R (Restricted), and the deliberately non-trademarked X (children not admitted). The flaw there was that a substantial number of people thought "M" was more restrictive than "R." So it changed to GP (General audiences, Parental guidance suggested). But that looked like "General Public." So it became PG.
That worked very well at first. There were serious films that got G ratings (
2001, the original
Airport, True Grit, Rio Lobo, The Andromeda Strain, Fiddler on the Roof, and the original Planet of the Apes, among close to 200 G-rated films between 1968 and 1972), and there were non-pornographic ones that got X ratings (e.g.,
Midnight Cowboy and
A Clockwork Orange).
But then, producers started gaming the system. On the one extreme, we got a whole genre of "dumb movies rated G for kids," and on the other, we got such artistic masterpieces (or is it
masturpieces) as
The New Erotic Adventures of Casanova. Pretty soon, only PG and R were available for mainstream movies, and producers felt they had no choice but to aim for PG, regardless of the subject matter. So PG became so swollen that it had to fission, spawning off PG-13. And NC-17 was added, in a not-terribly-successful attempt to allow an X-equivalent that didn't carry connotations of pornography).
The biggest mistake, in my opinion, was
the stubborn refusal to give reasons for ratings until the system had already been gamed nearly to the point of irrelevancy.
In a perfect world, the movie ratings system would be as it was at its inception: ratings would carry
no positive or negative connotations. And it would be treated as
nothing more than a guide for parents, as Valenti had intended.
**********
Back to the matter of swearing, comics have raised the depiction of swearing without actually saying anything obscene to a high art, (known in the business as "grawlixes"), and nobody was better at it than the man who first coined the term, Mort Walker, creator of
Beetle Bailey.
There's a lengthy passage in David Gerrold's
The Galactic Whirlpool about Starfleet curses. Pretty much the first page of Chapter 9. The key paragraph is
Scatological, sexual and religious-based curses, of course, were regarded as the work of amateurs. To be worthy of respect, a curse should arouse simultaneous sensations of pain and laughter in the listeners; it should bring tears to the eyes; indeed, a truly inspired oath should create ripples in the stress field itself and make all listeners within three parsecs turn around and stare in shock and admiration. A mild Starfleet curse should curdle an egg in its shell; a strong one should do it before the egg has even been laid.
Obscenity in literature (or in conversation) is like hot spices in food. And "fuck" and "motherfucker" are the "Creole Torpedo," i.e., cayenne pepper. But not many people like
all their food to have Scoville ratings north of 25k.