Youre exactly right but ...they? Who do you mean?
The purpose of terrorism is not the deaths, but the fear - the terror. That's the key differentiation between a politically motivated murder (Jo Cox) and terrorism (eg 9/11, the tube bombings etc). In the former, the chap had a very definite target, in the latter, the terrorist didn't care who was in building or train, it was merely to highlight that you're never safe from harm, they will attack indiscriminately.
However, to answer your question, 'they' are the media. They fan the flames so much. The only way we can make a stand is by not retreating into our shells. The best example recently was the Nice attack, where eyewitnesses said folk were back out on the street the next morning, business as usual.
@JonS 'keeping a stiff upper lip and carrying on' does not mean turning a blind eye and being all liberal about it. The public should carry on regardless; the authorities should come down on the perpetrators with an iron fist.