This crime AGAINST some Danish women stemmed from the ideas of Eugenics. No doubt about it. However, it also was fed by obsolete ideas of women and sexuality. In both cases it was an attempt to keep society free of "degenerate individuals" which meant people who suffered from inherited illnesses, especially of a mental character. To let these "sub-humans" breed would be to endanger society and that had to be stopped at all costs.
It happened in the beginning of the 1900th century and officially it stopped in 1961 when the infamous habit of interring women who were considered "retarded" ended. Up til then the morally suspects – ie "lose" women – ended up on the small island of Sprogoe (: Sprogo). Men were sent to another island by the name of Livoe (: Livø). Part of this must have been for punishment of "immorality", but the main reason for this cruelty was the wish to protect the society at large against "bad, defected genes". For them to be allowed to have children was a fight which they were bound to lose. Their reality was that they were not let lose from the island without being sterilized and those of them who already had children most often lost the right to even see them. Also because these children were put up for adoption and were expected to break off connections with their immoral mothers.
Some of these women left the island on their own which cost them their lives: They set out on an attempt to escape by swimming. However, none seems to have succeeded in this dangerous exploit. What is so sad is that what earned the women the name of "retarded" was their way of living. To be a woman and to have lovers was in itself an indication that they were mentally defective. It is a backward way of thinking rooted in old fashioned considerations about women and sexuality. One's wish to think that this happened several hundred years back in time is assailed by facts: It did not end until 1961 which means 9 years before the "Redstockings" started their feministic actions which went on to the 1980'ies.
One may wonder at the reasons these women were considered fitting inmates on an island like Sprogoe. However, but what brought them there is not different from some men's life style. A man who had a child out of wedlock was not interred the way a woman was likely to be. And it is ironic that the island sometimes swarmed with men visiting it in the hope of meeting some of these easy women. Nobody seems to have thought the thought that someone setting sail and venturing out on an erotic expedition to meet immoral women was just as bad as she was supposed to be for less.