I don't know if he really meant that the mob doesn't kill innocents as much as he means that they don't kill randomly. They also don't kill anybody based on what color t-shirt they're wearing. Also, old school mobsters at least, don't wave a flag telling people what they're into. They don't have 'colors.' The mafiosi who do stick out like that are seen as dangerous idiots (think Gotti). Amongst many gangs its common to talk about your affiliation and crimes. Some even make raps about it.

More anecdotally, imagine your average gang member. Could you see him speding 30 years of his life pretending to being mentally ill? I think that shows the difference.

Some of the dying families may just be gangs now, but the survivors are definitely a diffferent type of more developed criminal organization.

That being said, there were tommy gun drive bys during prohibition. Also, the sicilian mafia uses a lot of bombs, which do take civilian casualties.