The root problem here is child abuse. Anybody abusing children, or financially supporting the abuse of children, is doing a seriously bad thing and this is what should be illegal.
I'm highly skeptical that images on a hard drive can cause the abuse of children. That's the same kind of logic people used back in the 1970s to argue that playing D&D and listening to Kiss were going to result in a whole generation of Satan-worshippers.
You could show a non-pedophiliac person the entire contents of that hard drive, and it wouldn't arouse them or make them want to go abuse children. Wouldn't make me go abuse kids. I'd probably cry a lot and go volunteer to help some kids[1]. So I am not convinced that the contents of this guy's hard drive are going to result in more kids being molested somehow.
If anything, I think the opposite may be more likely. Access to porn is correlated to a reduction in rape. I don't know if this extends to pedophiles, but it sure seems entirely possible: https://www.psychologytoday.com/blog/all-about-sex/201601/ev...
Would I want my kids hanging around somebody with a hard drive full of that stuff? Probably not, but I also wouldn't want them hanging around supporters of certain political parties either, and I don't think they should be rotting in prison indefinitely with no trial.
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[1] I already do volunteer work; no need to send me illegal porn in order to get me off of my couch