[hippoman]

The probability of one kid being killed or seriously injured in this one school in, say a year is nearly zero so it won't happen and everyone will think it's wonderful. But if all schools do it all the time, you'll start to see some fatalities and brain damages where rules would have prevented them and people will start saying "let's forbid high forts with concrete to fall on" etc.

Anecdotal story. As a kid playing in the street I ended up under a moving car. The only reason I'm alive is somebody alerted the driver in time. We don't notice rare accident deaths, but we do notice pervasive safety measures (don't play on the road even in a culdesac anyone?)