The evidence for previous impacts is strong, even if there is a little uncertainty as to exact chronology. These previous impacts occurred in a far less populated and urbanised world. Today increasingly mega cities are situated in the littoral zone and the resulting tsunamis from oceanic impacts would be globally catastrophic. To ignore the very real risk, even if it is low, would be the height of stupidity.

http://elib.sfu-kras.ru/bitstream/handle/2311/1636/03_.pdf;jsessionid=CBA11409F1A8B01C8ADE7E38FDE6754E?sequence=1