Supporters of a federal law passed earlier this year aimed at eliminating online sex trafficking say it has already led to a significant drop in online advertising for sex. But critics say the law is merely pushing the trade further underground, and they hope to get the law overturned.

The law, known by its House and Senate titles, the Fight Online Sex Trafficking Act and Stop Enabling Sex Traffickers Act, or FOSTA/SESTA, was perhaps best known for persuading the advertising site Craigslist to discontinue its popular personal ads earlier this year. But the law's main target was more explicit sites like Backpage — which the feds seized shortly before the bill became law — that were alleged breeding grounds for trafficking and other abuses.

FOSTA/SESTA clarified a so-called safe harbor provision of the 1996 Communication Decency Act that said internet sites could not be held responsible for user-generated content. It specified that sites could be targeted for activities like child exploitation and sex trafficking.

The law took effect in April, but supporters say it is already having an impact.

"The sites that had been marketing children are not operating out and above-board anymore and that's a huge success as far as we're concerned," Carol Smolenski, executive director of Ecpat-USA, a nonprofit group that fights child exploitation, said in an interview with CNBC's "Deadly Rich."

Early indications are that 60 to 80 percent of U.S. online sex advertising volume has disappeared, according to Rob Spectre, a New York-based consultant and programmer who works with Ecpat-USA and other anti-trafficking organizations.

Beyond trafficking, online hookups have led to some truly tragic outcomes.

Texas millionaire Jake Clyde "Jay" Merendino was slain in Mexico in 2015, his body found in a ravine. His throat had been slashed, and he had been stabbed multiple times.

"It was brutal. This was stab, after stab, after stab," FBI Special Agent Eric Van Houten told "Deadly Rich."

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In 2017, a federal jury in San Diego convicted David Enrique Meza of "foreign domestic violence resulting in death" in Merendino's killing.

Meza, who is serving a life sentence, was a gay porn actor who had advertised his escort services online for $100 an hour.

"Hott (sic) Hispanic Star available for Guys and Girls – 22," the ad read. "I aim to satisfy your every fantasy."

So began a two-year relationship in which Merendino thought he had found true love. But prosecutors said Meza, who unbeknownst to Merendino had a girlfriend and a child, used Merendino as a "sugar daddy." When Meza's two worlds were about to collide, prosecutors said, he killed Merendino and attempted to cover up the crime.

It is impossible to know whether Meza and Merendino would ever have met had FOSTA/SESTA been in effect in 2013. The site where they met is still in operation and has not been accused of wrongdoing.

But critics of the law say regardless of whether it might stop isolated abuses, the law is fundamentally flawed.

"Would it be positive if the government took away the internet and phones because they've been abused," asked Tara Burns, a trafficking survivor and former sex worker in Alaska who now lobbies for safety and protections for those in the sex trade.

Burns says the drop in online sex advertising is hardly an indication that trafficking is being reduced. On the contrary, she says, sex workers are being forced into older and more dangerous ways of marketing their services. While she says it is too early for hard statistics, she is hearing more and more stories like those of a Las Vegas sex worker who had peddled her services online until the new law passed.

"Unable to advertise, she turned to working for an agency and was assaulted by a customer they sent her to," Burns said. "The casino security at the hotel detained her and threatened her with prostitution charges for six hours. She was left with missing teeth, two black eyes, and many bruises, unable to make money to get back home or pay for housing there."

Rather than restricting advertising, Burns says what she calls "consensual adult sex work" should be completely decriminalized. That way, workers would feel free to report illegal activity such as trafficking without fear of retribution. In Alaska, Burns successfully fought for a law granting immunity from prostitution charges to victims and witnesses who make good faith reports of illegal activity. She calls the law — the first of its kind in the nation — a "big first step."

Others are fighting FOSTA/SESTA more directly, on constitutional grounds. In June, a coalition of groups led by the Electronic Freedom Foundation filed suit in federal court in Washington claiming the law violates the First and Fifth Amendments, and seeking to have the law overturned.

"The law has already muzzled countless online speakers and led to closure of many online platforms that hosted their speech," the suit says.

The plaintiffs say they also oppose trafficking and other forms of exploitation.

"But," the suit says, "FOSTA will not reduce such practices; to the contrary, it only makes matters worse."

Could stricter laws have prevented Jay Merendino's grisly murder? Decide for yourself. From the producers of "American Greed," an ALL NEW episode of "Deadly Rich" airs Monday, July 30 at 10pm ET/PT only on CNBC. Watch!