Holland has some of the worst statistics for trafficking and crimes against prostitutes. Legalizing did not help improve conditions for sex workers. It simply attracted criminal gangs who brought in young girls from poor countries, often under false premises. Germany had similar problems, with child prostitution rising significantly. Amsterdam has just spent a significant amount of money buying up brothels to try to clean up the red light district which has become over-run with crime. They figured it was cheaper just to shut these places down than to keep trying to police them.
We should work to end this dehumanizing practice, not condone it.
Sweden has a good model. Prostitution is legal, but purchasing sex is illegal. Under such a system, prostitutes have full protections under the law, but the government is able to keep out a lot of the unwanted aspects that accompany legalized prostitution, such as trafficking, drug gangs, violent crime and increased disease and poverty.
http://www.usatoday.com/news/world/2008-03-16-sweden-prostitution_N.htm