Stolen bikes

People should be able to ride however nice a bike they like and not have to worry about it getting stolen. In the real world, and before any thefts have occurred, it's good advice to tell people not to leave bikes like that lying around, but after the fact it's definitely not a good thing to say. Telling people they're stupid for having done it is also completely unnecessary, as they'll already be telling themselves that in a way that has much more impact.