Free Internet porn is "like taking heroin," while online cheating websites can also lead to sex addiction, Gray said.
Gray, whose books including the original 1992 classic have been published in 50 languages and sold 50 million copies, is also worried about feminism, which he blames for spiking divorce rates.
"The reason why there's so much divorce is that feminism promotes independence in women. I'm very happy for women to find greater independence, but when you go too far in that direction, then who's at home?" he asked.
In an interview with AFP, Gray said widespread feminism in America holds back sales of his books here, while other parts of the world - he cited Australia and Latin America notably -- are more in tune with his basic message.
Men and women come from different planets, and the two sexes should stop trying to behave similarly, and embrace their own natural personalities, according to Gray.
"The most resistance I get to my message is in America. Wherever feminism has a strong hold, there's resistance to the idea that men and women are different," he said.
"When you go to Australia, for example, there's a very clear knowledge that men and women are different."
Gray also cited Latin American countries as places where "they love my books."
In Europe, he said his biggest fans are in France.
"I think it's because France is a romantic country, the language is more romantic, people care more about relationships," Gray said.
- Impact of technology -
The 62-year-old - who says he has saved "at least" hundreds of thousands of marriages over the last two decades -- meanwhile was ambivalent about the impact of technology on relationships.
Being able to meet people easily online has its pluses he said, citing notably the number of divorced people in their 40s and 50s who seek out former friends and partners from their younger days.
But he voiced concern notably about two online trends: Internet porn, and the huge success of so-called cheating websites, where users can hook up with others seeking illicit affairs.
"With free Internet porn, there's a massive addiction happening... just millions and millions of people are experiencing their sexual satisfactions through total fantasy," Gray said.
"The effect that porn has on the brain is like taking heroin."
Cheating websites, while providing real physical sexual experiences, are equally dangerous to real, long-term loving relationships, the author cautioned.
Sites like www.ashleymadison.com and www.arrangementfinders.com go "along the same line of pornography," he said. "When you have impersonal sex.... 'It's OK, here are these cheating wives, men, they want to have sex with you.'
"So you go have sex with someone that you don't know and someone you don't love... impersonal sex does promote addiction to sex," he said.
The California-based author and counselor meanwhile said he thought the famously liberal and fun-in-the-sun western US state had more divorce precisely because life is so easy here.
"Freethinkers want to go to California... They're experimenting with new things, so there's a lot of feminism here. You're at work all the time, naturally you start having affairs at work, and you get divorced," Gray said.
"California people are experimenting with new ways... I don't think therapy's the answer for everybody, I just think they need more therapy here."