I can think of three things which could possibly combine to form the 10%:

1. Outliers. People whose family culture has not changed since the 1800's and still practice it. These are no doubt uncommon statistical outliers, but they surely do exist.

2. People who do think it is wrong, but have low self-control and/or substance abuse problems, which makes them do things they are later ashamed of.

3. Immigrants. Immigrants from other places with other cultures can hardly be expected to adopt Swedish culture on this issue overnight – these things most likely take generations to be fully ingrained.

So yes, it is a “taboo” – it isn’t accepted at all.

School nurses and daycare personnel are trained to keep a lookout for any signs or stories from children, so anyone who does it will have to do it with the premeditated aim of doing it without anyone finding out, or else someone will find out. As I said, it is an ingrained social norm, not simply a thing which one does not talk about.

I would only add that the change in social norm can be seen already from 1958 when all school corporal punishment were banned. Seems rather reasonable that it took then two generations for family culture to not only change, but make it illegal as well.

Same in Germany, if a kid goes to a doctor with bruises or other physical damage the kid has to explain to the doctor what happened and the parents will be told to not interfere