70% of the earth is covered by oceans or seas. So the odds of one of these things even happening over land is less than 1 out of 3. And then to occur over an area of land that is actually somewhat populated is even much smaller that that. At one every 50 to 100 years or so, most of which will occur over water or desert (e.g the Tunguska event) I'm like Alfred E. Neuman. "What, me worry?" If these space rocks are too small for us to track with current technology, I say, "Let's do nothing!" Even this last one that against all odds did occur near a city caused no fatalities, for crying out loud.