Don't use this. Tax Fix / Flickr, CC The revelations about massive National Security Agency snooping in Americans' phone records and Internet activities appear to be shocking, but they aren't.

The reason programs like these exist and persist isn't that the government keeps them secret. It's that our lawmakers tell the public they are necessary to achieve a goal of zero terrorism, which might well be true — and the public considers that a good enough reason.

Sen. Dianne Feinstein (D-Calif.) offered this very succinct justification for the phone records dragnet, in which Verizon and apparently all the other major cellular providers hand over all subscribers' phone records to the government: "It's called protecting America."

Both the public and politicians have been clear: The goal of policies on terrorism is not just to reduce terrorism deaths but eliminate them altogether. Lately, we've been getting pretty close. Over the last five years, Americans' annual odds of dying in a terror attack have been just 1 in 20 million.

If we hope to maintain that record, we had better not have any false negatives in our search for potential terrorists. If the government can't miss any terrorists, how can it not have a massively overbroad surveillance infrastructure that snoops on all of us?

The perverse impact of zero tolerance for terrorism doesn't just show up in surveillance. It's the reason we all have to take our shoes off at the airport, that Boston shut down for a day after the Marathon bombings at a likely cost of over $100 million, and that we invaded Iraq.

We don't think about other social ills this way. Nobody says we should have a goal of zero heart disease deaths or zero auto accident deaths, because that would be nuts. We balance the objective of saving lives against other considerations, like cost and individual rights and the fact that bacon is delicious.

We should apply this cost-benefit approach to terrorism too. This approach would allow us to say that the phone records dragnet can be a bad idea even if it saves lives. But the big resistance to that analysis doesn't come from Congress; it comes from the American public.

Update: As Radley Balko notes, there are promising signs; public polling on terorrism has shifted in recent years to reflect a decline in public alarm. The time might be more ripe now than previously to push back against the expansion of the antiterror apparatus.