The second principle for a temporary demand-side fiscal program is to implement policies that have a large "bang for the buck." Even with agreement on these two principles, designing a temporary demand-stimulus package is a challenge. In general, temporary policies have effects that are more difficult to predict than those from permanent changes.
This argument is conceptually appealing, but in practice its foundations are rather shaky, to say the least. More specifically, I think that it would be extremely difficult to iron out the impact of asymmetric shocks via an active fiscal policy.