For example: think about speed bumps. Sure, we could just blame any drivers who crash into pedestrians in parking lots, but by adding speed bumps, we are reinforcing what people already know --- that speeding through parking lots can be dangerous.
Same thing with seatbelts --- you know that annoying chime that won't stop until you've buckled your seatbelt? Why do we need that? Why not simply blame any drivers who crash? Because it reminds people to do what they already know they should be doing. It reinforces safe behavior. It helps to reduce a burden on society --- the negative effects of fatal car accidents.
So I have a hard time whenever I hear someone say 'the problem isn't guns, it's the people who use them', because I think that's only part of the solution. Should people be allowed to purchase firearms "same-day" at gun shows? Should people be allowed to purchase and own as many guns and as much ammo. as they please? Is there something wrong with at least discussing possible reforms to make it more difficult for people to buy guns?