His assertsion about the number of wrongly convicted people are very wrong.I would say that around 80% are "users" whereas the rest have usually stumbled across it (this is very obviosu btw: there is not often a fine line). A lot of the defence is "it was a virus" so it is one of the first checks and has been the case in only one example as I recall.
We deal with all sorts of computers weekly & I have never identified CP on any of the machines that cross my desk (bar the odd image or 2 come across whilst browsing legitimate pron sites)
In terms of the origins: a lot of the mild abuse is "homebrew" with a small proportion of the worst images being homemade. The majority of extreme images are, from their context, commercially produced.
I cant say much about the children being forced or not (or comment on the argument of whether they are innocent or not) because I am biased due to my job and because it is wholly subjective (actually I deliberately emotionally detach from such thoughts to allow me to do my job fairly). And finally because I am involved purely in the technical side and have not met any abused persons :)
I am a bit worried to say any more: it really is grazing close to a line here (silly laws ;)). Im well on the right side of said line (i'll add) but....
EDIT: edited slightly after chatting to a colleague :)