Consider this question in another context. If I allege that you have committed a crime without providing evidence, should you go to prison if you are unable to prove that you didn’t?
Browsing a dark web is one of Tor’s primary features, i.e. providing access to onion services. Despite the way media typically frames it, a dark web is neither good nor evil, it is merely a network much like (and usually within) the internet.
Just like the rest of the internet, Tor’s onions contain plenty of websites for legitimate purposes and plenty of websites for nefarious purposes. I don’t have any information to suggest percentages but people choosing to access a dark web does not automatically make them bad actors.