"... possession of child pornography could be illegal is in my view indefensible. Some people might raise their eyebrows at that last one, ..."
The thing is, that child pornography exists at the scale it does mostly because some extremely vicious people make a lot of money out of it. They make a lot of money out of it because there is clearly a demand. That demand is manifest by the sickos in possession of those "documents". And meeting that demand requires the abuse of children.
"The possession of documents should never be a crime in a free society."
I'm certainly sympathetic towards that ideal - but I'm prepared to make an exception if that possession links directly to grievous harm (in this case to children).