It shouldn't be THAT much of a reach that De Meo would drink blood.
If he wasn't in the mafia he probably would have been a serial killer.
He was heading down that route before the mob gave him an outlet for it.
Name any mobster and 9 times out of 10 they have never even personally got their hands dirty on a hit, and if they did, it was either the impersonal method of shooting someone or as part of a hit team.
De Meo dismembered bodies, and by all accounts he liked doing it.
They used to casually eat slices of pizza while they sawed an arm off.
Come to think of it, Chris Rosenberg was another budding serial killer whose homicidal tendencies were harnessed by the mob.
