Well, there are definitely forms that are irrational, but there's also the perfectly rational factor of having to account for feedback loops.

We don't have to consider that shifting resources from lightning death prevention to terrorism prevention will increase the base rate of lightning strikes; we do have to consider that a shift in the other direction can increase (or perhaps decrease) the base rate of terrorist activity. It is thus inherently hard to compare the expected effect of a dollar of lightning strike prevention against a dollar of terrorism prevention, over and above the uncertainties involved in comparing the expected effect of (say) a dollar of lightning strike prevention against a dollar of large asteroid collision protection.