There is one imperative that is common among all life on Earth: survive. It is ingrained into our core. Makes us get up every day to go to school, work, and in some cases war.
Until people get to a point where they have full security or no fear of death, they will always be willing to sacrifice morals for a bit more life. If that's what we consider barbarianism, then I'm afraid it will be a long time before that goes away.
Yes, no fear of death sorts it all!
Yes, survival instincts are engraved in all of us but it doesn't have to come at a cost of another. In fact, we ensure survival even more by working together with other people.
It depends on the situation. The concept itself should hold true from the smallest to the most extreme sense.
Could be as simple as keeping the extra dollar that was from incorrect change. Just because it's small doesn't mean it's insignificant. And how can that not be applied towards defending ones family from harm? One can justify that we are only fighting evil. People find reason to justify their actions; actions that benefit themselves. This is, in effect, finding the best way to survive for the current situation.
What you are putting forward, however, is the benefit of having foresight. I wholeheartedly agree. Unfortunately, not everyone has this or the situation just doesn't allow enough time for it's fruition.