I'm sorry I rephrased your statement and changed the meaning. Pet in this case means what you like doing the most when it comes to greed. What you like doing the most is hate greed.

Greed is my pet's aversion... Although the subject is about how the pet hates greed, pet is the object in this sentence. The definition of pet according to Google is: noun 1. a domestic or tamed animal or bird kept for companionship or pleasure and treated with care and affection. "the pony was a family pet" used as an affectionate form of address. "don't cry, pet, it's all right" adjective 1. denoting a thing that one devotes special attention to or feels particularly strongly about. modifier noun: pet "another of her pet projects was the arts center" synonyms: favorite, favored, cherished, dear to one's heart; More verb verb: pet; 3rd person present: pets; past tense: petted; past participle: petted; gerund or present participle: petting 1. stroke or pat (an animal) affectionately. "the cats came to be petted" synonyms: stroke, caress, fondle, pat "the cats came to be petted"

It means "my own favorite" like a pet animal would be.