This, in turn, reminds me of a situation a few years back in which my toddler nephew was walking around the patio with a real-life hammer in his hands. His mother (my sister-in-law) was totally nonchalant about it, although you could cut the tension among the rest of us with a knife.
Admittedly my mother-in-law was a "worry wart" to the nth degree, and could be a real pain in the ass about kids safety (more than once I had to politely advise her to mind her own business when she questioned such things as a 3 year old eating raisins - "They can choke!" or giving a 5 year old Children's Tylenol - "It will ruin their livers!) but she wasn't the only one who was alarmed. My father-in-law who was the complete opposite of his wife looked worried, and so did my wife.
Such events had arisen before though and we knew the mother didn't take kindly to advice about the kid, and that she ignored it anyway. It was obvious the three other adults were more worried about her reaction than the little lad swinging a hammer.
We were sitting around a glass cocktail table and when he started to swing the hammer and was thrown forward by its weight, I reached in and gently removed it from his hand; distracting him with a funny face or some gibberish. As expected, his mother responded something to the effect of "Oh, I'm Ok with it. I don't like to limit his freedom," to which I replied, "I know, but all I can see is the hammer breaking the glass table and him getting sliced up, or him somehow burying the claw in his head, and it’s driving me nuts. I can't stand the tension. He'll be OK without it."
His mother gave me a withering look, but I had the hammer and I guess she either knew I wasn't going to give it back to him, or would have felt stupid insisting that I did, especially since I was playing with him and he was fine about not having it any longer.
When the mother left the area to get something my wife and her mother said "Thank God you did that, it was giving me a heart attack!"
I very rarely interfere, in any way, with how parents deal with their kids. I may give them unsolicited advice if I think they’re not aware of a danger or concern, but I figure that they're only going to do it when I'm not around, so why waste my breath and possibly piss them off. This, however, was a case of preventing an imminent accident, and taking four adults of tenterhooks.
Explaining it as "I'm a nervous wreck about kids and accidents and it was driving me crazy!" seems to work on the rare occasions I've used it. When you take matters into your own hands you don't have to worry about whether the parents have the sense to listen to you, and what are they going to do? Wrestle the hammer, saw, or knife back from me and stick it in the kid's hand again? Pick up the kid and move him back to the middle of the street? Tell the kid to go and stick his hand in my dog’s mouth again?
I'm all for letting parents raise their kids the way they want, but when there's a really good chance the kid's going to get hurt, someone else's property is going to get damaged, someone else is going to get hurt, or everyone in the room is a nervous wreck, I'll act and worry about the fallout later.
I think with the case of the kid on the ledge, I would just turn around, walk away and say a prayer for the child. Trying to remove him from the edge would have been too dangerous a move in and of itself, and likely to trigger a defensive response in the parents. It's obvious from the photo that they knew where he was, so saying something like "You better watch your kid or he's going to fall a thousand feet to his death," probably would have fallen on deaf ears.
What drives me nuts is that people like my sister-in-law (and probably the folks in the photos) think that just because a disaster has never resulted, none ever will and that there laisse faire parenting has been repeatedly validated. Of course it's just a matter of time, before the disaster come about.
You can run 10 stop signs in a row and not have a wreck, but if, as a result, you conclude that stop signs are pointless, you are an idiot.