‘I understand the concept of the “movie-plot-threat”, but what is the alternative? To do nothing?’
Doing nothing (that wasn’t already being done before 9/11) would be better than what we have now.
Deaths from terrorism are so rare that it’s not worth doing anything to reduce them. In a typical year, at least 44,000 people die from medical errors in US hospitals. About 50,000 people die from motor vehicle accidents. Doing something about one of these might actually save some lives. How many people died from terrorist attacks in the USA last year?
Estimates of the number of people in the USA who died from obesity last year range up to 300,000 (I know, it seems incredible, but google for “death rates usa” or something similar). So your couch, if it’s temptingly comfortable, is about 200 times as dangerous to you as Al Qaeda is.
A comment from the Schneier blog.
This of course, also applies equally to gun ownership.
When you apply logic to these problems they can be put into context and then the right thing inevitably follows. When you think feverishly, reactively and at the behest of the news agencies, then you make mistakes of the sort that have created this dystopic nightmare scenario world that we are living in.