The answer lies in human psychology. And probably like the old observation about history, people who refuse to understand human psychology are doomed to be victims of psychological manipulation. How is it that even members of peace groups have now come to support US bombing? One lady framed the issue like this: "I request that we discuss and examine why the videotaped beheading of a human being is understood to be more egregious than the explosion (almost totally invisible to the public) of a human being by a missile or bomb fired from a drone."
There are at least four main reasons that explain why Americans care far more about the beheadings (thus far) of two Americans and one U.K citizen, than they care -- here's the polling -- about the thousands of foreign victims of US drone bombing. Here's how people are likely being manipulated into believing that more US bombing is the answer to such terroristic killings even when almost all military experts have admitted that it won't work and "there's no military solution":