You could say the same about any fairly unsecured transport network. There's countless bridges, buses, trains and stations worldwide that could cause a massive loss of life and there's virtually no security bar some token "No unaccompanied bags" notices. I suppose we should just be thankful that terrorists are not actually intelligent enough to figure it out.
The unfortunate truth of the matter is that whilst the threat of terrorism perhaps doesn't scare everyone, it certainly inconveniences everyone. Time is money, and the simple fact that these security precautions cost lots of it are helping them to win.