The linked study revealed that around 80% of hidden service visits were to paedophile websites.

Is 80% of internet traffic child pornography imagery? Are 80% of cars driven by paedophiles? If not, your comparison makes no sense really.

Also, Tor isn't public infrastructure. It's a largely anonymous group of people who have collaborated to form an anonymising network. Everyone involved who is aware of the above is knowingly enabling the sexual abuse of children, by allowing the perpetrators to hide behind their network.