First, there's an enormous amount of groupthink in that scene. Second, they abandoned their ethical compass -- do you remember when "An it harm none, do what you will" was central to Neopagan practice? I do -- and yet these people, most of them Neopagans, abandoned that in favor of death spells and invocations of demons against their political enemies. Third, they're getting increasingly obsessive about the supposed war in the Otherworld, and equally so about their "Tower time" persecution fantasies. Put those together and mass suicide becomes frighteningly possible.