Addressing Risks

A few years ago, I read an editor's introductory column in a scientific journal. He argued that America's response to terrorism was disproportionate, not to the magnitude of (then) recent terrorist attacks, but to the attention we given to graver threats. Environmental damage and species loss, he argued, pose more serious harm than terrorist acts on the order of the 9/11 attacks. This argument commits the "dominant risk" fallacy:

To reason that if risk A is greater than risk B one should pay no attention to B, whatever its absolute size, is like telling a person who has cancer not to seek treatment for a broken arm.

- Richard Posner, Catastrophe: Risk and Response, pp. 116-7

In many cases, one would be able to address both risks. It is only when one cannot attend both that one should ignore risk B. But suppose that one chooses to ignore risk A. Is there now a compelling to ignore B?