That's really not the point. Whether or not you know what you are doing, you are the mechanism by which child porn is distributed. From a Bayesian perspective,

That's really not the point. Whether or not you know what you are doing, you are the mechanism by which child porn is distributed. From a Bayesian perspective, you can just decide how "at fault" you are. If you're in a firing squad of 10 people and 1 guy has blanks, there's a 90% chance you're firing real bullets at the guy in front of you, even though you may have no real way of knowing whether you're actually firing blanks or bullets. Either way, there's the objective fact of what you are doing (which is independent of your knowledge of the fact) and the degree of your complicity in the action. The parent is saying that they are uncomfortable with knowing that there is an x% chance they are aiding in the distribution of child pornography. There's an argument to be made that providing infrastructure is very different from active engagement, but it's bizarre to pretend that because you can't objectively know what each packet contains that you are therefore absolved of all knowledge of the situation.