I would argue that Sweden does have a minimum wage since, from wiki - "There is no minimum wage that is required by legislation. Instead, minimum wage standards in different sectors are normally set by collective bargaining." I think that having a government lobby for your interests is the same as a collective doing so.

Looking at countries with no minimum wage, or, to put it another way, no formal organisation(s) to lobby for the rights of workers, it is clear that the results are less than savory (hint: the only country this applies to is North Korea) - http://en.wikipedia.org/wiki/List_of_minimum_wages_by_countr...

I think that the core issue is that the majority of people expand as much as they can until something stops them, which is why formal agreements are necessary at this stage of humanity's development. Few people are conscious enough to act fairly in the absence of law. I think that the long term solution to creating a society where a minimum wage is not necessary is education and a culture of personal development. When people stop outsourcing their morals to authority, they will make the right decisions.