I would bet that maybe not, but a disproportionate number of darknet websites is. P(darknet | child porn) might be low, as you are suggesting, but P(child porn

I would bet that maybe not, but a disproportionate number of darknet websites is. P(darknet | child porn) might be low, as you are suggesting, but P(child porn | darknet) >>> P(child porn | clearweb), in orders of magnitude.