"Sex is like swimming," said Ian Kerner, a licensed psychotherapist and nationally recognized sexuality counselor. "I'm not so worried about adults who know how to swim. But where do 13-year-olds who want to learn about sex and start masturbating go? They need to learn how to swim in a world of porn, because it's not going anywhere."

But it is getting harder for kids to distinguish between real and porn sex.

What kids learn from porn

Earlier this year in Denmark, a sexology professor caused a bit of an uproar when he called for pornography to be shown in schools. It would be preferable to sex ed classes that were "boring and technical, where you roll a condom onto a cucumber," he told Danish public broadcaster DR in March.

"We know from research that a vast majority of teenagers have seen porn at an early age, so it's not a question of introducing youngsters to porn," the professor, Christian Graugaard, said. What he wants is to make sure teens "possess the necessary skills to view porn constructively."

"We should strengthen their ability to distinguish between the media's depictions of the body and sex and the everyday life of an average teenager," Graugaard said. "They should become conscientious and critical consumers."

Kerner regularly lectures at schools and colleges about the differences between porn sex and real sex. He said students often ask him about explicit sex acts and whether they'll be expected to perform them.

"The concern many grown-ups have is that young people will see it and want to do all of these things," said Dan Savage, author of a nationally syndicated sex advice column and host of the podcast "Savage Lovecast."

"It's not so much that the more extreme porn instills desires, as it instills anxiety. These kids are convinced or afraid that things they've seen are expected of them -- and they may not be interested in, or looking forward to it. It's assuring and freeing for young people to be told that."

Savage added, "Sex education needs to include porn now because the genie is out and can't be stuffed back in."

Can porn benefit adult relationships?

For adults, the wider world of porn created liberation, a sense of relief and even communities, Savage said.

"One size fits all wasn't fair," he said, because it didn't help those interested in non-normative body types, desires or kinks. "Non-normative desires make people feel like freaks or alone."

Both Savage and Kerner suggest porn can be a great tool when dealing with discrepant desires or libidos, such as in the case of new fathers, who can turn to porn for variety or stimulation. They suggest couples can, and should, use porn as a way of introducing erotic stimulation into their relationships.

Porn can even be a good coping strategy when you're stressed or depressed. "You can sometimes discover or explore taboos through porn that they can't in real life," Kerner said. "The real issue is when it's kept a secret. Studies show that the main deleterious effect is not so much the content itself, but the shame and secrecy that contextualized its use."

So long as porn is made with consenting adults, Kerner says not to judge yourself or others for their interests or fantasies. "It's not an indication of a personality characteristic," he said. "A wife discovers her husband is into Asian bondage stuff. 'Is that who he is? Is he a kinky person? I don't know him anymore!' "

Savage said that porn can make it easier for partners to remain faithful to each other.

"We have a hard-wired desire for variety. Porn allows you to scratch that itch without physically cheating on your partner," he said.

"I don't like to see people get divorced for stupid reasons. You set your marriage up for failure if you have unrealistic expectations -- like you're never going to look at or see another naked person outside of your marriage. Policing another person's sexuality, expression or interior life is a relationship form of terrorism."

With the shift away from the plain old nude photo, those who lose out are the young people who are just starting to understand sexual desire -- and the adults whose tastes were satisfied by a centerfold, the experts said.

"It makes people with normative desires feel panicked the way it used to those with other desires," Savage said.

Nothing left to the imagination

"Back in the day, Playboy was the forbidden fruit," said CNN contributor Mel Robbins. "It was titillating. It was exciting. It was forbidden. What Playboy stood for and what their appeal was centered on something that was taboo back then. Has everything shifted? Absolutely."

Opinion: Why is Playboy giving up nudity?

"Playboy was sort of the Norman Rockwell of porn," Kerner said. "These days, we have not pictures, but motion pictures. Nothing is left to the imagination. You don't have to fill in the blanks."

According to Kerner, the top online sex search terms are actually "pretty vanilla."

"When you look at those terms, I've noticed men approach porn like they watch TV. They have things they always like to turn to," Kerner said. "Sometimes people are interested in things more distinct or a little more of a fetish -- but it doesn't take more and more and more. Of course, that's the rule. Some patients have very rigid fantasies that are dark, but that's the exception, not the rule."

Robbins laments the amount of nudity her children see every day, just by spotting magazines at the grocery store or scrolling through their Instagram feeds.

"It raises the stakes as a parent," Robbins said. "You have to actively be framing all of the imagery and the innuendoes kids are being bombarded with, whether you realize it or not. And if you don't realize it, you're being naïve. Even when women are clothed, look how the women are posing.

"What's exciting about the times we live in is that people can explore the things that get them off. But there are really scary things about that. It's a very scary and frustrating time to be a young woman dating in a major city. Apps like Tinder, Grindr -- and the behavior it fuels. You need to have a sense of self-awareness. Are you engaging in the behavior because you truly want to, or because you think you should?"

In the end, "the most satisfying and amazing thing in the world is having an incredible sex life with the partner that you're with -- in person, in a committed relationship," Robbins said. "It doesn't matter how good the video is, how good the photograph is. Nothing will compare with the magnificence of that at a soulful level."