In Sweden prostitution was legal in both sides of the transaction before the law, so your question is strange as there was no legalization going on. As to why

In Sweden prostitution was legal in both sides of the transaction before the law, so your question is strange as there was no legalization going on. As to why the stigma has increased, it is a documented fact that it did, established by the evaluation that was done some ten years after the law was introduced. Swedish political climate regarding the question being what it is, the investigator saw the worse conditions for sex workers as something that was a positive outcome.