Andrew, those "occasional" explosions you are referring to would be much less "occasional" in the absence of those pesky authorities.
Actually, terrorism is surprisingly rare in this country. Apparently we're doing a pretty good job of keeping busy in other countries the very small cadre of people who possess, all at once: the will, the organizational skill, and the resources.
The TSA and the rest of the security apparatus in this country has proven itself, repeatedly, to be completely incapable of preventing terrorist attacks. The TSA fails tests constantly. Until recently there were trivial, obvious, openings in their procedures. They had fancy microwave body scanners, but they could not reliably connect a boarding pass with a person. Bruce Schneier used to (and perhaps still does) take great delight in pointing these out. The FBI is unable to find a single domestic terrorist plot that is not made up almost entirely of FBI agents. Nobody knows what the CIA is up to, but we can take it as given that they're doing it very very poorly and with great violence because this is their unbroken track record.
We find out about credible plots, 100% of the time, after they are carried out.