This is not uncommon. We saw it in the Japanese, Germans, and Italians in WW2. To pretend we didn't is to do a disservice to history and the needless sufferings and deaths of many. Throughout history, it was repeatedly shown that murder and torture come easily. Because of that, I always avoid the term "humane", since it implies that humanity is, as a whole, kind and good by instinct. There is nothing further from the truth. Sociopathology is more prevalent than we'd like to admit, and we are all capable of it, as the infamous Milgram Experiment showed us.
Human nature is why so many of our ancestors were either the victims or the inflictors of various forms of torture and horrific deaths since the world began. There is only a thin veil between civilization and the primordial beast, and although we don't always understand why a sociopath chooses to step over to the other side, we know that they never return. If a pit bull, who's always been friendly, suddenly snaps and kills a child, we don't try to rehabilitate it. We put it to sleep. We know that the dog has crossed the line, and there is no turning back. Some decisions, whether by man or animal, are irrevocable.
The biggest mistake that we can do is to not study history, or take it seriously. As George Santayana famously said "Those who cannot remember the past are condemned to repeat it."
Although we are horrified by the terrorists' actions, we should not be surprised. Nor should we be surprised to see the articles that discuss the terrorists' recruitment of US youth. The terrorists appeal to anyone with sociopathic leanings. You can whitewash their attraction with the labels "mesmorizing", "deceiving", "gullible", but the fact remains that every American knows what terrorists are and what terrorists do. If they are signing up for the program, it is because deep down inside there is a ravening bloodthirsty beast who wants to dominate, has no regard for the lives or feelings of others, and enjoys mayhem, torment, and subjugation.
If we are able to stop a recruit from going overseas to join the terrorists, they should immediately be locked up and put under psychiatric evaluation for that very reason. If you are willing to go to such lengths to become a terrorist, there can be no room for you in a civilized nation any more than there is room for fire ants at a picnic.
As for the terrorists overseas, Obama's obvious and stated reluctance to commit ground troops continues to make us look weak. And if we are perceived as weak, with our porous borders, how encouraging to a terrorist. If we don't commit to ground troops, the only effective alternative is, as the Green Berets say, "Kill 'em all and let God sort 'em out." Or, in this case, Allah is welcome to them. I don't think he's what they think he is, and I have a very strong suspicion that Allah and his terrorists will be sharing the same living quarters and it will make the tropics look like Antarctica.