> but the idea that he actually didn't know what MU was being used for

Is that a reason to be held liable? Isn't the whole point of the DMCA that we realize that every open service that transfers bits will be used illegally by some, so as long as the service provider acts on takedown notices they cannot be held liable for the actions of their users?

> or that he cared about preventing it

They had a special tool for content creators which gave them direct delete access to everything on MU. This goes above and beyond the DMCA.