This week in theaters, the violent monster bash “Clash of the Titans” has been… This week in theaters, the violent monster bash “Clash of the Titans” has been deemed acceptable for teenagers aged 13 and older. But if kids under the age of 17 want to check out the blatantly silly “Hot Tub Time Machine,” they’ll have to bring a parent or guardian — the film is rated R.

It’s a well-established Hollywood double standard that a film can gorge itself on blood and guts and remain suitable for young teens, but drop more than one f-bomb or show something more than cleavage and it’ll be banished to the morally bankrupt junkyard of R or, in some extreme cases, NC-17.

It’s a ratings system unique to American audiences, and one gleefully deconstructed in the 2006 documentary, “This Film is Not Yet Rated.” In the movie, the Motion Picture Association of America, which oversees all American film ratings, is portrayed as an almost cultish organization — an anonymous squadron of moral crusaders bickering behind closed doors which films are worthy or unworthy of a mainstream audience’s attention.

The board members, according to the film, are mostly older parents. Their standards of evaluation, or lack thereof, are kept secret. Their suggestions for cuts, should a film be deemed too inappropriate for a mainstream audience, often undermine a film’s most powerful scenes — usually sex scenes.

From both an intellectual and evolutionary standpoint, this seems ridiculous. In most instances, sex is good and violence is bad. But for the MPAA, this truism is inverted. Sex becomes obscene, while violence is accepted as commonplace.

In spite of this, parents from sea to shining sea take the current rating system seriously. It took the best of my fourth grade coaxing abilities, for instance, to get my parent’s permission to see the PG-13 “Doctor Dolittle” (apparently Eddie Murphy doesn’t tone down his language for the animals).

Not to sound like a snob, but Europe, that land of old churches and Smart cars, has devised better systems. The British Board of Film Classification, for example, ranks films based on their potential for, “desensitizing a potential viewer to the effects of violence, degrading a potential viewer’s sense of empathy, encouraging a dehumanized view of others, suppressing pro-social attitudes, encouraging anti-social attitudes, reinforcing unhealthy fantasies, or eroding a sense of moral responsibility.”

Sounds a bit puritanical, but their hearts are in the right place — the object is to protect children from desensitization, particularly from desnsitization of violence. Which is how these ratings should go: “the birds and the bees” talk is inevitable, but the “violence is a part of life” talk should hopefully be avoided.

If I were king of Hollywood (and I’m working on it), the ratings would go as follows: give G ratings to movies that couldn’t possibly damage a child’s psyche (aka 90 percent of all G and PG movies), PG to movies with a couple f-bombs and cases of slight nudity, PG-12 (because PG-13 seems too arbitrary) to movies with nudity, sex and/or some — not excessive — violence, and finally, R to movies with violence strong enough to engender, in the words of the BBFC, a “dehumanized view of others.”

This isn’t to say that violence is inherently corrosive. The list of blood-drenched classics is long enough to fill plenty of movie columns, and when examined with maturity, filmic violence can teach us valuable lessons. It’s just that onscreen gore seems much more capable of inflicting mental or emotional harm than onscreen sex does.

Don’t get me wrong, I’m not suggesting that kids forgo “How to Train Your Dragon” in favor of “Hot Tub Time Machine,” but it’s the battlefield, not the bedroom, that’s most likely to leave a scar.