Of course there are edge cases. Reality is continuous, not disjoint, and thus any attempt to impose a line will inherently create edge cases. What you are mis

Of course there are edge cases. Reality is continuous, not disjoint, and thus any attempt to impose a line will inherently create edge cases. What you are missing is that the case of inaction (not permitting it) also creates bad things. You can't make a situation without bad, all you can do is attempt to minimize the bad. Note that the "ideal" (as in maximum social benefit) amount of bad things happening is not zero. Preventing bad things always comes with a cost, there will always come a point where additional preventing of bad things causes net harm. Consider, for example, nuclear power. It has basically been regulated out of existence in the US because of the standard that radiation exposure must be as low as reasonably achievable. The problem with this is that it doesn't result in safer nuclear plants, it results in plants that run on different power sources. Natural gas? Approximately 10x the risk (and that's not counting climate effects.) Oil? Approximately 10x the risk of gas, thus 100x the risk of nuclear. Coal? Approximately 10x the risk of oil, thus 1000x the risk of nuclear. The expected (and observed) safety benefit of the regulations is negative. And to preempt the inevitable "Fukushima!", that was political. The expected death toll of staying put was approximately zero. The city was evacuated, killing hundreds, for no good reason.