Thankfully, no, I never had to kill someone. But having spent 4 years in the Corps myself, I was trained and prepared to do so. Would it suck? Maybe. I can tell you this, if my life, or my wife´s life was on the line, or my kids, Í wouldn´t hesitate to pull the trigger. Multiple times. (Big fan of overkill) And I doubt I´d feel too bad about it afterwards- probably lose some sleep over it, yeah, maybe for a night, but then I´d get over it.
There is a difference in murder, which I couldn´t do, and justifiable homicide, which is what this Marine did. And I´d like to think I wouln´t lose any sleep over a justified killing, ESPECIALLY if it was my life (or my family´s) on the line.
And exactly how else does one resolve the situation? 4 thugs jumped out of the car at him- there was no time to say `stop, stop! Let´s hold hands and sing kum-bay-yah and resolve this peacefully!` It was a split-second decision, and his apparently far superior training kicked in (he probably didn´t even realize it) and it was over before anyone knew what happend. I say he probably didn´t realize it, because in these situations, the training is designed to do just that- get you out or contain the situation without thought, just instincts. Which apparently this guy had plenty of.