Well, speaking about the Australian summer really.
Australia is a particularly hot place, and parading around without clothing on is a good way to get burnt and promote development of skin cancer (assuming of course that you don't use any sun screens, but I dare say the sort of person who wanders around in the glaring sunlight without a shirt on doesn't pay too much attention to sun safety).
I don't know if I'd paint everyone who does this with that brush. You're looking at it from your own cultural perspective. Over here it's not generally seen to be reckless or taboo, so you can't really come to those sorts of conclusions because they don't hold the same here. Granted, we do have higher incidence of skin cancer, but I myself do it and I'm very conscious of wearing sunscreen. Basically, if it's just "idiots" that do it in the UK, you can't then apply that same logic to Australia.
I also don't buy into the idea that we need to "protect the children". There's nothing inherently stressing about a child seeing breasts. It's only an issue when they've been socialized into thinking it's taboo. They will react the way their parents react, and be stressed if their parents are stressed.
