Passive mobs need light to spawn, and they only spawn on grass. If the aggressive mobs are spawning, then it must be night and the passive mobs will only spawn near torches, pumpkins, glowstone, etc....
Both mobs exist, I can assure you that. Look up "the Westies" and "hells kitchen" Both mobs generally only exist in New York but I know for a fact both have factions and families in other states as...