Ah a drive by troll. How refreshing. Today I am bored enough to respond.
Once there was a Mongol army of such power and ferocity that it came close to wiping out western civilisation as we know it. So you are suggesting we should worry about that happening again? Are you really worried about getting nuked today, or tomorrow? I'm not. But then again I associate the frequency of an event with the risk of it reoccurring. I guess that by your reckoning we should not, and that all events that have ever happened are equally probable in the future, so we should treat them all the same.
I will now start worrying about herds of velociraptors raging across major cities causing carnage and destruction. After all, it is about the same level of hysteria as complaints that the one-time mob attack of a paediatrician is relevant 15 years after the event.