Note: This article is part of an effort to raise awareness of sex trafficking during National Slavery and Human Trafficking Prevention Month.

Over the past 15 years there has been an increasing awareness and concern about the scourge of sex trafficking. At no other time in history have so many people acknowledged the problem and taken active measures to stop the abuse. Evangelicals, in particular, have played a prominent role in attempting to end this cruel form of exploitation.

Yet all this effort is being undermined by a misguided campaign intended to advance human rights and individual freedom: the worldwide movement to legalize prostitution.

Many Christians would be surprised to find how the public’s attitude about prostitution has changed over the past several decades. For instance, a poll taken in 1971 found that just 14 percent of Americans thought prostitution should be legal, compared with 86 percent who thought it should be a crime. In 2015, though, Americans were about evenly split on the issue: 44 percent of Americans think prostitution should be legal while 46 percent think it should be illegal. (Democrats tend to support rather than oppose legalization [50 percent to 40 percent] while most Republicans oppose rather than support legalization [54 percent to 34 percent]. Independents are evenly split, 45 percent to 45 percent.)

The legalization effort gained significant momentum last summer when the international human rights organization Amnesty International adopted a policy that supports the “full decriminalization of all aspects of consensual sex work.” Now Amnesty International lobbies governments around the world to decriminalize both prostitution and its solicitation.

Like many legalization advocates, Amnesty International believes that prostitution itself is a “victimless crime” and that by bringing the vice out of the shadows it will “lessen the risk of abuse and violations they face.” The reality is just the opposite. The more prostitution is legalized, the more it leads to the enslavement of men, women, and children for the purposes of sexual exploitation.

Supply and Demand of Prostitution

To gain a better understanding of the connection, let’s start by considering the question, “Why does sex trafficking even exist?”

Supporters of prostitution might claim that because it is illegal, few women are willing to enter the market for sex work. This leads to an undersupply of prostitutes, thereby providing an incentive for sex traffickers who are willing to force women into this illicit labor. Under this view, if we would simply legalize the practice then the supply of female “sex workers” would increase and the need for sex trafficking would dissipate.

Of course, the reality is just the opposite: Countries that legalize prostitution report larger human trafficking inflows than countries where it is illegal.

This connection between prostitution, both legal and illegal, and sex trafficking is exceedingly well established. As Donna M. Hughes has noted, “evidence seems to show that legalized sex industries actually result in increased trafficking to meet the demand for women to be used in the legal sex industries.” Melissa Farley adds that “wherever prostitution is legalized, trafficking to sex industry marketplaces in that region increases.”

This should be obvious to anyone with even a basic understanding of both prostitution and the economic concept of supply and demand.

Making prostitution illegal has the beneficial effect of artificially decreasing the supply of men who would solicit a prostitute. Some men who would otherwise be interested in paying for sex are unwilling to pay the additional “costs”—the risk of being arrested and exposed as a “john.” Legalizing prostitution, though, would increase both the existing pent-up demand and the new demand that would result from de-stigmatizing the vice.

There is also the supply side of the supply and demand equation—the supply of prostitutes. The supply side of prostitution has never been able to meet the demand for a rather obvious reason: few women want to sell their bodies to strangers. Prostitution is disgusting, degrading, and corrosive to the soul. (This is something that tends to be missed by supporters of legalized prostitution, many of whom have never come in contact with an actual prostitute.)

This is one of the hundreds of reasons why women do not voluntarily engage in sex work, and why the supply of non-coerced prostitutes has been—and always will be—naturally low. The disadvantages associated with prostitution are so numerous that many women would refuse to engage in sex work even if no other options for survival were available.

Real World Effect of Legalization

So by legalizing prostitution, we substantially increase the demand for sex work while minimally increasing the supply of prostitutes. It’s not difficult to see where this leads. The suppliers of commercial sex acts (i.e., pimps) are not able to meet the demand with the number of willing prostitutes, so they have even greater incentivize to force people (mostly women and young girls) to engage in “sex work,” whether legal or illegal.

Basic economic theory tells us this is what we should expect to find—and the evidence from social science has confirmed that this is exactly what happens. As Hughes writes in the Journal of International Affairs, “The transnational trade in women is based on supply and demand from sending and receiving countries. Countries with large sex industries create the demand and are the receiving countries, while countries where traffickers easily recruit women are the sending countries.”

Legalization advocates ignore the reality that increasing a country’s “sex industry” by legalizing prostitution naturally leads to sex trafficking. This is not only economically intuitive, but also apparent to anyone open-minded enough to look at the evidence.

Amnesty International and other advocates of legalized prostitution may have the best of intentions. But their altruistic motives cannot overcome the economic realities of the sex slavery trade. Because the entire incentive structure is designed to force exploitation of the weak and vulnerable, prostitution can never be a victimless crime. That’s why the effect of legalization is not freedom for the oppressed but the creation of more slaves.