[ghaff]

A lot is familiarity.

I was in Detroit for an event a couple years ago. A number of us didn't really feel safe after dark and there were a couple incidents that other attendees experienced. Part of it was the general reputation but we also just didn't really know.

Whereas I'll walk down 5th avenue in Manhattan at two in the morning with no real concerns though I'm being more alert than if it were noon.

As you say, it also wouldn't take many bus/subway incidents to make me go: "That's a nope from now on."