I haven't seen it mentioned here or in the obituaries, but Peter started the RISKS Digest in 1985 partly in response to the Strategic Defense Initiative (SDI, "Star Wars") which proposed a space-based anti-ballistic missile system run autonomously by computers [1].
Another response was the formation of Computer Professionals for Social Responsibilty (CPSR) [2]. Peter was an early member, and many early RISKS submissions were by CPSR members.
Peter's letter to readers about the creation of RISKS in Issue #1.01 [3] mentions SDI and CPSR (it's long, scroll down)