allah's holy warriors are always busy, isis or not.
Yup. And no amount of security can stop them. Even the most totalitarian security state would not be able to completely eliminate the threat. There are ways to combat terrorism - but visible security measures at airports and border crossings are not one of those ways. Such security does nothing to prevent terrorism; at best it might move it to other targets - if bombing a plane is hard, then the terrorists will bomb trains; if bombing trains is too hard, they can bomb buses. Or stadia. Or concerts. Or shopping malls. Or restaurants. If you put enough security checkpoints in place to scan every person entering any popular public place, then the lines for scanning become viable targets. Security checkpoints are a strategy that cannot possibly succeed.
You can't stop small numbers of determined people from committing terrorist attacks by checking IDs, X-Raying or searching bags, making people walk through metal detectors, or forcing passengers to take off their shoes before boarding a plane. But you can give paranoid citizens a confidence boost with these measures, and you can be seen to be
doing something (even though it is something utterly futile and pointless); and you can win votes by doing that. Ultimately, the only result of all this "security" is that blameless citizens are less free, and more inconvenienced. The money wasted on the TSA would be much better spent on the CIA, and FBI counter-terrorism departments; But such expenditure is invisible to the public, so it wins no votes.