I'd like to suggest

https://www.torproject.org/eff/tor-legal-faq.html.en

which was written by my colleagues at EFF. (It doesn't mention particular legal theories that may help exit node operators, though I think CDA §230 and DMCA §512 might be among the laws you're thinking of that have historically protected ISPs, since ISPs have resisted being classified as common carriers in the U.S.)