In more simple English, this sentence could be rewritten as:
Everyone was shocked to learn that such an important person in the field of ethics was capable of the kind of trickery he used to get his job.
The first option does no make sense because utilitarian is an adjective. The third option is not a possibility because no one would be shocked at a proper use of decorum. The last option does not work because larceny is not used to defect.
He starts off by eating little things like flies, but then he goes onto eating bigger things and those things can symbolize growth in a person for vampirism.
