Looking at the map of countries that legalized prostitution one can see a paradox - Sweden seems to be one of the harsher countries in Europe, even though they're leading the world in terms of overall liberalism. Why is this the case? Is there something in Swedish culture that strongly disapproves of "sinful" entertainment?
There are of course general concerns regarding prostitution, like trafficking and bad social implications, different countries has reached different conclusions here.
The thing with Sweden is that we have a strong culture, at least in regards of media, to search for injustices and oppression. Strongly connected to this is the common view that women in general are victims of male privilege and oppression, where for example phenomena like the #metoo campaign gain huge traction and is on the front page of news papers for months.
In this context, the idea that women can be seen as a sexual commodity to be bought by men is often seen as a preposterous. The gender factor in regards of prostitution is also a contributing factor to why it is illegal to buy but not to sell sex in Sweden: Male buyers are seen as taking advantage of vulnerable and distressed women, while female prostitutes are seen as victims of male privilege and oppression.
Simply put, prostitution is strongly looked down upon in Sweden specifically because we have strong feminist movements (in different flavors and types) while prostitution is seen as both symptomatic and reinforcing of a structural male oppression and sexualization of women.
The Wikipedia article Feminist views on prostitution summarizes the position of those who are opposed to prostitution as follows:
Anti-prostitution feminists hold that prostitution is a form of exploitation of women and male dominance over women, and a practice which is the result of the existing patriarchal societal order. These feminists argue that prostitution has a very negative effect, both on the prostitutes themselves and on society as a whole, as it reinforces stereotypical views about women, who are seen as sex objects which can be used and abused by men.
(Other views exist, too – see the article for more details. Furthermore, there are of course positions on prostitution that are not feminist in nature.)
It is this view, of prostitution being harmful to prostitutes and to society as a whole, that dominates in Swedish politics. Accordingly, paying for sexual acts (Swedish sexköp) is considered behaviour comparable to assault and is therefore banned. (Note that offering sexual acts for payment is not a crime.) It is no matter of liberalism, because there is no right to harm others.
The core problem with legalizing prostitution is that in countries like Germany that have legalized prostition a significant portion of the prostitutes are still victims of human trafficing. The German newspaper Spiegel describes the situation:
According to various studies, including one by the European Network for HIV/STI Prevention and Health Promotion among Migrant Sex Workers (TAMPEP), 65 to 80 percent of the girls and women come from abroad [to Germany]. Most are from Romania and Bulgaria.
Axel Dreher, a professor of international and development politics at the University of Heidelberg, has attempted to answer these questions, using data from 150 countries. The numbers were imprecise, as are all statistics relating to trafficking and prostitution, but he was able to identify a trend: Where prostitution is legal, there is more human trafficking than elsewhere.
The Netherlands chose the path of legal deregulation two years before Germany. Both the Dutch justice minister and the police concede that there have been no palpable improvements for prostitutes since then. They are generally in poorer health than before, and increasing numbers are addicted to drugs. The police estimate that 50 to 90 percent of prostitutes do not practice the profession voluntarily.
Similar observations that a significant amount of the prostitutes in Sweden get mistreated led Sweden to forbid prostitution again in 1999 after having allowed it before 1999.