Having everyone he's close to except Cuthbert die at the cornucopia and then decide that if he can't protect any of them, he and Cuthbert might as well take down as many people as they can.

Yeah.

So far their kill count is Sherlock--whose head they shaved during the murder to punish him for trying to steal Effie's boyfriend and also for making Cuthbert look even dumber than usual during their mutual distruction--and soon Effie Lottie by accident.