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.
If you want to make that argument (which may well be correct), you should back it up with facts. How great is the risk of a child drowning in a pool of the size in question? How much does a fence reduce that risk? How expensive is a fence? And so on. Of course, those who argue on the other side should also back their claims up with facts, and the burden of making the case is properly on them to show that the law is needed.
But that isn't an argument I'm interested in having. I was merely arguing the principle that regulation of safety hazards on private property is not necessarily unacceptable (and the remark that raised the hackles of the libertarian radicals was merely that I understood the requirement for a fence, as opposed to the requirement for a building permit).