Why is the national security so weak?

The story that really applies that this might be true, has to be the attempt on Christmas day by Umar Farouk Abdulmutallab, who attempted to take down the northwest airlines landed in Detroit by placing a bomb in his pants to blow up the plane. Even being suspected of being a part of a terrorist group and having his visa application rejected, still their was no way to prevent him of this tragedy that could have happen. Warnings from his father telling the U.S. embassy one month before stating "My son is around bad people who could be plotting an attack ," should have been a huge red flag. I mean this man was in Detroit as cold as it is without a coat to me that's suspicious enough and no luggage, what other signs is needed. I'm not for judging anybody for what they have on or how they look because as a black man knowing that feeling of being judge and label is ludicrous, even worse for people who practice this religion but doesn't believe in hurting people are getting stereotype on a daily basis for a group of people's wrong doings. You would think because of previous attacks and attempted conspiracy's attacks the national security would be more prepare for such a senseless act like this, especially when our terror alert red just a few years ago. I think you can blame the people was working that day for not being more alert and also the policy's we have in place, maybe its not secure of enough, or being cheap on funding it because profits are going to economic issues we have going on. Either way something has to be done, I have never took a plane but this affects me even if it never hits home because if attacks keep happening and it apposes that we have a weakness for protecting our country and opens potential new problems. Why is our national security so weak right now?With new policies they plan on putting in, will it make flying into nervously strict experience.