Some reasonable points here, but I think there is one very solid argument in favor of making possesion of child porn illegal (and also explains the sense of applying strict liability here): if mere possession is illegal then demand is reduced. Effectively, the legislation aims to destroy the market for child porn thereby preventing abuse/exploitation of children. There's definitely room to debate whether illegalizing…
Except that's not true. Previously in Sweden, production and distribution of child porn was illegal, while possession was legal. But ten years ago or so, through lobbying and some shrill "think of the children!" campaigns, our politicians decided to change it and make possession illegal. This actually required constitutional change, since the basic freedom of the press had to be changed.
And the change was made, even though a lot of professionals objected to it. Lawyers were upset, because they generally thought you shouldn't tamper with the constitution unless you had really good reasons to. The police were negative, because they couldn't see how it would help them catch more actual criminals. The prosecutors were negative since distribution and production are enough to catch the criminals you want to catch. And the journalists were against it for the reasons linked to in the article. But think of the children! And so the law was changed.
Now, 10 years afterwards, the result of the change is exactly as the professionals predicted: The law change hasn't done anything. There's no great reduction is child porn cases. The people they do catch are all guilty of distribution or production, possession is irrelevant. Journalists are pissed and more cautious of the subject. And there's been a few idiotic cases where people have been convicted even though its obvious they shouldn't have been. Like a manga critic who was reported by his pissed ex-wife, and when the police searched his place they could kinda see how two books (out of a huge collection) maybe depicted underage people, so they had to arrest him. I think he got acquitted after appealing though, it seems higher courts have a more sane view of the matter.
And then you have more common worries, for example what about digitizing old photo albums? I have photos of myself, one year old, bathing, naked. Maybe I should just burn that photo to be sure? What about taking digital pictures or movies of your own children, and they happen to be naked somewhere. Post to Facebook? Or oh shit, delete as fast as you can?
So, making possession illegal did not in any way change the situation for actual pedophiles distributing actual child porn. They're still as guilty as before, and still breaking the law as before, but regular people are affected by it, journalists are affected by it, and the copyright maximalists are using it to push their agenda. And that's a pretty strong argument for making possession legal again.