The worst they got up to was some toe nipping. I understand NYC banned them due to a rabies scare (unrelated to the actual ferrets?).
Ferrets are indoor animals. It's retardedly rare to have a case of rabies in a ferret, and due to their small size, rabies would ravage them VERY quickly. If a ferret got outdoors, they would likely not make it past 6 hours depending on the weather. Here in FL, during the summer, considering they have no way to perspire, a ferret would succumb to heatstroke in less than 30 minutes.
And yes, toe nipping does happen. I had to teach my family that biting of any kind was strictly verboten, and if they happened to be a nip recipient, they were to immediately scruff the fert and snip them on the nose. They learn VERY quick, and we've been bite-free for a long time.
The absolute worst part of being a ferret owner is "accidents." I do my very best to ensure they use their litter boxes, but sometimes they'll get the inkling to just go when they damn well please. It's usually in a nondescript corner, but cleaning in that tight space is the hard part.
I love my ferts with all my heart. They're great pets, they are very affectionate, incredibly intelligent and they know you by your voice. Kalifornia is just doing the typical knee-jerk BS they've always done.