Captain Blood was apparently a big hit when it was released despite staring the then-unknown Flynn. It was also nominated for a best-picture Oscar. But by today's standards it is very tame.
And it got me thinking about how much "adult content" entertainment needs to have to be entertaining. Captain Blood is entertaining with almost zero adult content. But the movie Rush was also entertaining but had nudity, bad language, and violence (in the form of car crashes and fist fighting).
Back when Captain Blood was made, entertainers had no choice. The U.S. used an obscenity standard that was based on English common law which required (according to Wikipedia) "any material that tended to 'deprave and corrupt those whose minds are open to such immoral influences'" and that was interpreted to mean the most sensitive individuals in a society which meant children. Which meant that all entertainment had to be okay for children. A series of Supreme Court decisions, ending with Miller vs. California in 1973 redefined obscenity (which did not enjoy First Amendment protections) as work that "applies to prurient interest" and lacks "serious literary, artistic, political, or scientific value." That last part has been a pretty big loophole and a lot squeezes through it judging by the dregs of our culture. So your novel can have the raunchiest sex scenes and the most graphic violence and assuming it has literary or artistic value, there's no problem. So pretty much the law no longer regulates what "adult content" entertainment can have.
So this is where the word "gratuitous" comes in. What if in Captain Blood there was a sex scene, with nudity, with the prostitute. What if during the sword fights there was blood gushing everywhere. Would that be gratuitous? It obviously wasn't needed since it's a fine film without it. But the violence of Saving Private Ryan was there for a reason and the movie needed those graphic, bloody scenes to make its point about war and the "Greatest Generation."
My opinion on "adult content" is probably pretty typical: if it's needed, use it. In my science fiction novel Rock Killer the "F-word" is used three times. Why? Because I felt in those bits of dialog only the F-word would suffice to convey the meaning I wanted to convey.
In my Adept Series novels I have tried to keep the "adult" content" to a minimum. Swear words are mild, sex is off-screen (so to say), and while the violence gets bloody it's not belabored. But there are things some might find offensive. For instance, in the first Adept Series novel, Hammer of Thor, there's a scene where a doorman at a speakeasy says: "No niggers, chinks, or Irish." (I had a conundrum about this at a public reading and bowdlerized myself.) In fact, the "n-word" appears three times in Hammer of Thor and I just used it in my unnamed work in progress (which is set in 1881 when racism was ubiquitous).
I'm not one that gets easily offended but there are people who are. Should we write for them? No. We should write for our intended audience. "Adult content" should never be gratuitous but should be used when it's needed for the story and the message. Sex, violence, and bad language have their place. And some readers want gratuitous sex, violence, and bad language. As with all writing, remember your audience and you probably won't go wrong.