In 1999, Sweden passed legislation to criminalize the purchase of sexual services. This legislation, known as the Nordic Model, understands that the most efficient way to combat sex trafficking and prostitution is to reduce the demand for paid sexual services.Legislation based on the Nordic Model has proven itself to be an effective deterrent to potential sex buyers. Iceland, Finland, and Norway have adopted the Nordic Model and have witnessed significant declines in all forms of prostitution, including sex trafficking and child prostitution. Recently, the European Parliament’s Women’s Rights and Gender Equality Committee recommended that the European Union adopt the Nordic Model.

What is the Nordic Model? (an brief explanation from Equality Now website)

Legislative Models for Addressing Prostitution

In an attempt to regulate prostitution, several countries have legalized it. Germany, Holland, and parts of New Zealand and Australia have adopted this approach. However, all these countries have subsequently witnessed a vast increase in sex trafficking and other forms of prostitution, including the prostitution of minors.

Though Holland legalized prostitution in 2000, only 1,000 of the country's estimated 30,000 prostituted persons were able to meet the legal criteria to become licensed sex workers. Moreover, the government and non-profits reported a steep rise in illegal forms of prostitution, especially child prostitution.

Germany legalized prostitution in 2001. In 2010, government officials reported sex trafficking into Germany had increased drastically. The increase was attributed to legalization, which made Germany a more attractive market to traffickers and pimps.
You can read more information here and here.

Prostitution is legal in New Zealand and parts of Australia. In Queensland, Australia (where prostitution is legal) it was found that 90% of the prostitution was illegal, and that legalization had only served to strengthen and enrich pimps and managers of brothels. Prostituted people in New Zealand reported that legalization hadn’t protected them from violence, and women’s organizations expressed their concern over the many young girls who continue to enter into prostitution. You can read more information here.

It has been demonstrated that prostitution cannot be regulated, and that legalization does not bring emancipation to the women and men trapped in the sex trade. Legalization turns pimps into managers and businessmen and sex buyers into clients, and legitimatizes the abuse of those in prostitution.

By legalizing prostitution states declare that it is acceptable to purchase the bodies of some women (usually poor and marginalized women), and this attitude contributes to creating a cultural of prostitution that negatively affects the progress of all women.

Need more reasons to support the Nordic Model?
Ten Reasons for Not Legalizing Prostitution and a Legal Response to the Demand for Prostitution – Professor Janice G. Raymond