In the first millennium there was no airport security and a large number of Viking raids on Britain.

In the second millennium airport security was introduced and many fewer viking raids took place

In this millennium with greatly increased airport security there have been no viking raids on any part of the British isles.

Why was this downvoted?

See dalke's reply to me below for an actual response:

http://news.ycombinator.com/item?id=1852670

If you have the technology to make a bomb, just take it somewhere else crowded that's less defended. Or do something like the D.C. sniper did years ago.

If you calculate the lost man hours of productivity on airport security, we're getting killed everyday.

There are definitely ways to avoid this, but it's probably best discussed outside this forum.

If they had caught a bunch of people, don't you think they'd be singing their praises from the rooftops?

I agree with your point that there is no evidence to suggest it makes us even a little bit safer.