The ability to upload illegal content to the web long predates "Web 2.0"
Even on a college campus with a decent network, you ran the risk of getting kicked off if you misused the Broadcast address. Why? Cause there were software and hardware limitations that would bring down or cripple the network.
All that has been overcome. And now everyone on the planet can broadcast 24x7 almost for free.
This is the big issue.
If every neuron in the brain had Broadcast capability how would such a brain work?
Some food for thought - https://www.edge.org/response-detail/10464
forums, social medias, meme sites, youtube, comment sections everywhere, hn or its brother reddit, etc...
"Web 2.0" changed nothing in that regard except making asynchronous requests possible with AJAX, allowing sites to become more complex and allow for realtime updating. But yeah, people have been posting gore, porn and CP everywhere since the dark ages.