Legalizing prostitution leads to human trafficking
That has been found true in some European venues, mostly because of poorly constructed laws and regulations. Yet stricter laws in Denmark and Hungary governing human trafficking and strict licensing for prostitutes has led to much lower ratios for human trafficking in both countries with stable numbers of professional prostitutes. Keep in mind human trafficking is not limited to prostitution, but also as source of low cost labor, including household servants and field workers as examples.
On the other hand, poverty in rural and small cities of eastern Europe remains as source issue for human traffickers, inclusive of voluntary participants. Organized Albanian criminals import Romanian, Albanian, Croates, Serbs, Cypriot, Hungarian, Bulgarian, Czech, Polish, Russian and other ethnic women to the US for prostitution and have no need to coerce anyone into the trade. A working girl here can earn enough in six months, touring the US, to go home with enough money to open a small business, buy a home and gain more education, earning 4-5 times as much money as they would earn in western Europe during 2-3 years in the same trade.
My niece went to Hunter College for nursing. One of her fellow students, from Poland, also studying to become a nurse, on a student visa, claimed she was earning more than $150k annually on the side, working as an "independent escort." Untaxed underground economy. She returned to Poland after 4 years with a degree, credentials as an RN, and more money than her father earned in 3 decades. My niece told me while this young woman attended Hunter, she usually wore designer clothes my niece nor any of the other students could afford. Most of her fellow students lived in scrubs, working part time in hospitals and doctor offices.