It's not worth it. >99.9999% of people have good intentions and just want to go about their lives. That's why people go to the supermarket, to sports games, and all kinds of other places in public where we lack this kind of "security" and life goes on just fine. There are always going to be a few people who want to cause harm. You will never stop them all. And frequently, in trying to do so, you will give up your own basic freedoms (not to mention spend tons of money). If terrorists can get entire nations to to alter their behavior and live in a state of fear, they've already won and have caused far more damage than they would by blowing something up.