You're right, it's not in your culture. You've been trained to submit, to let your leaders think and decide for you, and the majority of your population are submissive followers. So it makes perfect sense that your adrenaline goes raging off the chart and you get scared of yourself when you have a small hunk of metal in your backpack.
I am proud to be an American, with the direction our US society is heading. Our founding fathers would be proud to hear people from the UK are terrified of this sort of thing.