A lot of child abusers also use the Internet, so you should stop using it. They also use storage devices, SSDs HDDs, we should stop using those as well. And they use electricity, a lot...
Most people have absolutely no need to use Tor, but it's clearly very useful for child abusers looking to not get caught. That study reported 80% of hidden service visits were to paedophile websites. This really is not comparable in scale to how electricity, the internet, storage devices, and so on, are used.
And clearly very useful for activists and journalists to not get imprisoned and tortured because they revealed things they shouldn't have.
But so is the "clear Internet", really. Sure there is a high proportion of innocent traffic, but if you think in terms of criminal activities, I am sure it is non-negligible. From copyright infringement to child pornography to revenge porn to harassment to unlawful handling of data. I have no numbers to back it up, but I'm quite sure a lot of crimes are committed on the "clear net".
And yet, it would be very unreasonable to shut the Internet down over this. Punish the person and their actions, not their tools.