The horror of the terrorist attacks rests not so much on the wounding and death of the victims as on the deliberate and hateful nature of the attacks. It is therefore prudent to separate the two aspects and consider them each.
The attacks were perpetrated by crazy young people using a murderous ideology to motivate and justify their actions. I say crazy because sane people do not deliberately murder people to whom they have no relation. The unfortunate reality is that at any given time there is always, in every society, a substantial pool of crazy people, some of whom could be tipped into violently hostile and aggressive action. Tribal ideologies, whether derived from ethnic identity, fundamentalist religion, injustice, or anything else serves to stimulate and justify such actions. but These crazies are not much different than, say, the anarchists of the late 19th century, the Slavic nationalists who engineered the assassination of the Austro-Hungarian archduke at Sarajevo in 1914, or the assassination of President Lincoln by John Wilkes Booth. But with modern communications and relatively easy access to guns, such crazies seem to have become more numerous and much more dangerous than ever before.
Is it feasible to shut down the communications that stimulate them? Certainly not directly, without losing our freedom of speech. Perhaps indirectly, by reducing the urgency and romance of their appeals through corrective measures to the misery that so many now endure in their lives, eliminating the most militant terrorists, and in general making the practice of terrorism more unattractive to the young--long term projects all.
Turning to the risks that terrorism creates, I have two thoughts. One is that in cold statistical terms terrorism adds very little to the general level of risk of physical harm that prevails. On an annual basis I imagine that disease, automobiles, fires, and natural disasters, even bicycles kill or wound many more people. My other thought is that many people, including the "experts" who advise, write, and appear on TV; the firms that sell equipment to police, paramilitary, military, and terrorist organizations; and of course the media themselves all profit from creating or perpetrating public hysteria about terrorism.