Asked about the trend toward "reprehensible protagonists" -- a la "Breaking Bad's" Walter White, "Boardwalk Empire's" Nucky Thompson or "Dexter's" serial killer -- Showtime Entertainment chief David Nevins offered a surprisingly frank answer.

"It's license," he told reporters at the TV Critics Assn. tour in July. "Pay cable, you take license. Your licenses are sex, violence and bad behavior."

Nevins omitted the other obvious one -- salty language, and those few words (thank you, George Carlin) that still can't be uttered on most of TV -- but otherwise, he was right. There are several less-ostentatious attributes that differentiate pay cable in particular and to some extent basic's raciest hours from broadcast TV, including the expanded running time of episodes, and nonexistent (or diminished) advertiser scrutiny. But it's sex, for better or worse, that frequently generates headlines or provokes controversy.

Granted, part of that may have to do with sex and nudity providing a clearer point of distinction from less liberated alternatives, as broadcast networks brave more explicit violence in programs like Fox's "The Following" or NBC's "Hannibal." By contrast, the U.S.' perceived puritanical streak relative to Europe has always made explorations of sexuality dicier, unless of course the material is being wielded as a sitcom punchline.

Another incentive to flaunt some skin may be that frontiers regarding violence have been shoved, some would suggest, about as far as they can go. After the "Red Wedding" on "Game of Thrones" or the artful blood splatters of "Spartacus" (which, to be fair, knew its way around a Roman orgy, too), it's less a question of topping what's been done than simply finding creative ways to push the same buttons.

Historically, violence seldom triggers the level of outrage from the usual suspects that sexuality does. The exception would be when entertainment collides with real-life events like last year's horrific Newtown school shooting, which inevitably produces fleeting hand-wringing but little concrete action from the entertainment biz and others about contributing to societal violence.

Chasing the boundaries of TV sex involves something of a moving target; seldom does a season go by without some newcomer braving uncharted territory, or at least finding a way to put old wine in a new bottle. HBO's "Girls," certainly, has drawn attention with its blunt portrayal of awkward sexual encounters among twentysomethings, including a sequence last season in which a male character ejaculates on
his new girlfriend after she specifically asked that he not. (An HBO spokeswoman had to explain to nosy media outlets that the sequence was "nothing more than a use of props.")

Showtime has tackled the topic head on with "Masters of Sex," a just-launched dramatic look at the career of real-life sex researchers William Masters and Virginia Johnson. The nature of those studies are depicted in graphic detail, with more nudity and simulated orgasms than you can shake a stress-test-wired dildo at.

"It was an irresistible topic for a premium television series," Nevins says.

License also helps account for why cable programs regularly push sexual bounds even in shows where the situations may be less than organic or central to the premise -- precisely because sex is something that can poke at overstimulated nerve endings and arouse a response.

This casual inclusion of sex and nudity -- almost in a "because we can" manner -- hasn't gone unnoticed. Los Angeles Times critic Mary McNamara, for example, chided esteemed dramas like "Game of Thrones" and "Boardwalk Empire" a few years ago for their habit of setting scenes in brothels, deeming it a gratuitous practice for the sole purpose of showing female flesh. "Maybe it's time to tone down the tits," she wrote.

On the other hand, a series like Showtime's "Homeland" has featured sexual encounters but also gone weeks at a time without them, the fundamental matter of thwarting terrorism trumping such dalliances and offering little time to pause for them. (The new season does include a liaison involving the central character's teenage daughter, another provocative area.) And full-frontal male nudity is definitely a more common sight in pay TV shows than it was just a few years ago.

Tellingly, some of these graphic depictions of sexuality are being overseen by women, including "Girls" creator Lena Dunham and Michelle Ashford, the showrunner on "Masters of Sex," which is based on a book by Thomas Maier.

Yet the fact that explorations of sexuality aren't limited to a male perspective isn't universally hailed as progress.

"I think women can objectify women just as easily as men can, unfortunately," says Martha Lauzen, executive director of the Center for the Study of Women in Television and Film at San Diego State U., who has studied TV employment for women -- both in front of and behind the camera -- since the late 1990s. "Quite a bit of (that objectification) is coming from the indie film world and seeping over into television."

Indie film, of course, continues to explore sexual themes. But the license exercised in pay cable -- closer to the feature arthouse than the broadcast networks, certainly, but still a relatively mainstream medium -- comes at a time when studios frequently soften sex in major releases, feeling the heat to avoid R ratings and thus expand the box office potential of their major releases.