What is the value of death? Against a society that highly values life, or perhaps has fewer citizens to sacrifice, the value of death is an enormous card to play.
One of the traditional ways to wage and win war was to kill as many of the enemy, as possible, as well as their families, while causing maximum destruction to valued property. Yes, ideally you surgically take out the means of continuing warfare, but that does not really stop an implacable enemy that is willing to fight hand-to-hand if necessary. The simple goal: intimidation and forcing the other side into abject surrender.
So it is with Muslim terrorism, the seemingly wanton disregard for the value of life while attacking those to whom innocent life has the most value. The more innocent the victim, the more horror in western civilization eyes. The greater the apparent randomness, the greater the fear throughout a western society that ANYONE is at risk. The greater the personal fear, the greater the intimidation of society. That of course is all intended by the Muslims to lead to universal dhimmitude subjection of non-believers, and even better to intimidate them all into conversion to Islam, with a penalty of death for continued insubordination. This is all well-laid out in everything taught from Madrassa schools to the hadiths to the Quran itself. It is merely a different warfare, couched in religious, theocratic, regimented absolutes.
Muslim terrorists, even at an estimated million, too weak to conquer outright, play on intimidation. Ultimately the Caliphate counts on infiltration and conquest by force to reach the goal of global domination.