This will never end. As long as countries like Iran (assuming Military Intel is correct) are supplying terrorists we are always at risk. Honestly, we could have been attacked any-time anywhere since 9/11. The recent attacks on Briton should have been a wake-up call to everyone. They always have had the chance to attack. Heck, for all I know, my neighbor could be a terrorist waiting for the go-ahead.
We live in a dangerous world. Nothing has changed since 9/11. We have always been in danger, what makes no any more dangerous? Just the small chance that the terrorist might have gotten chemicals?
I agree with celegorm though, there's always been the threat of terrorist attack. All we can do is hope they can be caught before anything terrible happens.
I live in Manhattan myself, and I have learned to accept things like they are. Sure, a terrorist attack would be horrible, and I would give anything to stop one from ever happening, but I also realize the risks of living in a city like Manhattan. They will be caught and killed in time, and the most we can do right now is pray and hope.