Good theory. That totally
could be an issue. Maybe sex work is like ivory, and not like, I dunno, all the other jobs human beings do! Or maybe not.
Luckily, we can check NZ, since they legalised sex work, and research has since been done to see what the answer was: http://www.gaatw.org/publications/SWorganising/NewZealand-we...
And actually, none of that is true! Actually it turns out that what really enables trafficking and the abuse of sex workers is situations where they can't go to the police, or where brothels have to hide their existence from the authorities entirely. Once you're legal and regulated, it's really easy for the immigration officials to show up and start checking paperwork.
> you'll still fail to have only the entirely above-board, willing sex work that the sex workers themselves would like.
Funny you should say that; again in the linked report it was noted that NZ does have an issue with that, but not from trafficked women, but rather from migrants. Due to anti-trafficking sentiment, the original law legalising prostitution banned people on temporary visas from working in the industry, which means people on temporary visas are the only sex workers in the country who can find themselves subjected to abusive work conditions while being unable to report it to the authorities.
It makes sense, of course; everywhere you ban sex work you create a shadow that victimisation can take place in.