I don't know about other parts, but in Sweden it was legal to disseminate between 1972 and 1980, while possession was banned through a constitutional change in 1999. What happened in 1972 was that the previous law that had limited/banned pornography (which had been under scrutiny and debate since the early 60's) was repealed completely, without retaining any restrictions on things like child pornography. AFAIK, production of child pornography was never legal though.

I suppose it's not unlikely similar things happened elsewhere as well. But in all cases I'd suspect it a result of an oversight rather than intent. I certainly don't think it's reasonable to interpret it as reflecting any kind of social acceptance of child porn.