You decide on a case-by-case basis, balancing the risks with the costs (material and otherwise) of reducing the risks.
I don't see why this is such a difficult concept to understand, but no one who's replied to me so far seems to get it.
Right! Risk analysis should be something everyone uses when making important decisions. For example:
I have a kid and am concerned he might run out into the street and get hit by a car, drown in my neighbor’s pool, be attacked by a dog, or kidnapped by a child molester. I think I’ll put up a fence in my back yard.
Why not let the parents be responsible for watching what their kids do? If you feel that you might not be able to keep an eye on them all the time buy a fence for your yard. I’m pretty sure that my pool is not going to wander off my property and drown someone on theirs. No one wants a child to die but inevitably, some will and the cost/risk analysis you cite above, in this instance is an undue liability to a private property owner for his/her neighbors decision to have children.
I think I 'get it' just fine.
It goes something like this:
The lemmings that nowadays pass for Americans can't be bothered to pay attention to the world around them. And the very last thing they will ever do is take responsibility for their own actions. They'll pretend that the world hasn't been and always will be a dangerous place. And when these naive fools bang their knees and stub their toes on the coffeetable of life, they go running and screeching like 3 year olds to mommy and daddy (ie, lawyers and government).
And mommy will say "There there, don't you worry your pretty little heads about that mean old man next door and his swimming pool/fast food/cigarettes/guns/dogs/diving board."
And so we go about 'balancing risks', which is a neat little way of saying trading safety for freedom. And it is assumed that my freedom is there for you to trade (its not). That I can't eat that donut because your @ss is too fat. That I can't have a diving board because you're too stupid to use it correctly. And so on.
And the next thing you know, the entire country is dumbed down and childproofed to the level of two year olds, which of course is justified by socialist medicine - if someone hurts themself, everyone else pays for it. Therefore everyone is going to have a say in your behavior, and they have decided its cheapest for them if you live your life in a straitjacket and are spoon fed gruel before you are sent to bed at a decent hour.