Do we need more security? Sure. But are we willing to pay for it? I'm not just talking taxes, but have you flown lately? Yes, I want to feel secure on an airplane, but if I have to go through things like that to go fishing, launch a boat, take a class, shop at the mall, etc...
Want a big impact? How secure is Silver Dollar City? Your workplace? The mall? Your school? Major trafficways? Sports arenas?
My point is that we are starting to "live in fear" because of the media attention. To me that's falling into the hands of those who do these things. That's what they want. I can't see myself doing that.
You are correct that the plan would be to blow up 50 dams and not just one. The problem is that providing security enough to have any chance to prevent such action would result in a shutting down of many of the things we take for granted, if it was even possible.