I also think waiting for "academic consensus" to act is not the neutral position it seems. Skepticism in the face of a pressing concern is not neutral, but instead acts to support the status quo. 
If we don't do something, more people will die. Possibly a lot more people. Academics have documented the dramatic rise in online radicalization.  Violent radicals themselves have described how online fora have pushed them towards extremism. So if you're going to argue a wait-and-see approach, I think you have to justify the bodies that will stack up in the meantime.
 E.g., https://www.amazon.com/Alt-America-Rise-Radical-Right-Trump/... and the many resources it points to.
Something you aren't grappling with here is the way the Internet has enabled previously-scattered terrible people to connect and self-radicalize. David Neiwart, who tracked various "patriot", white supremacist, and other fringe groups since the 90s, wrote a very readable book about how things have changed since then: https://www.amazon.com/Alt-America-Rise-Radical-Right-Trump/...
I definitely appreciate the early ethos of the Internet. It's a good founding myth, and I would like to work to keep things open by default. But if the worse 0.1% of humankind ends up not being able to host anything because otherwise they will work together to murder people, I am 100% ok with bending my "anything goes" bias a bit.
But at best, they had an incredibly rosy view of what was going on. E.g., looking back, a Twitter founder claims that in 2006 everyone "was cool": https://twitter.com/rasmus_kleis/status/974552443789836288
Given Gabriel's theory, that's obvious bunk. And having talked to some online community pioneers, abuse started pretty much from the get go. Look at all the replies I got when I brought it up on Twitter, for example. Story after story of early experiences of trolling, abuse, etc: https://twitter.com/williampietri/status/974847531317211136
There was (and is) a strong strain of technoutopianism, where we take the shiny new possibility and project a perfect future onto it. This goes back at least as far as the introduction of the telegraph, which many thought would bring about world peace: https://www.amazon.com/Victorian-Internet-Remarkable-Ninetee...
As Neiwart documents, though, many of the terrible people online today are intellectual descendants of the terrible people who were doing their social networking in person and via the mail: https://www.amazon.com/Alt-America-Rise-Radical-Right-Trump/...
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