David Ignatius at the Washington Post talks about the technicalities of the attack on Mumbai, and admits it would be hard to stop a similar attack elsewhere.
Many years ago - about 30 - I knew a retired combat colonel who remarked that terrorists wouldn't be able to kill innocent citizens if the citizens were armed to fight back. That was many years before the advent of the suicide bombers, and he might have modified his statement a bit, but if you think about it, the fact that whenever a Palestinian terrorist uses a method that doesn't kill him immediately some bystander does it for him does rather make the point.
Not everybody needs to walk around armed to the teeth. But yes, in cities with a reasonable random sprinkling of armed and trained fighters among the citizens, Mumbai-like attacks will be far less lethal. Sorry, but that's the truth.