Because killing is a threat to the species' sustainability and progression, therefor destructive.

The phrase "point of view" exemplifies precisely the issue with good/evil. It's malleable to an agenda. The followers of such destructive teachings will of course justify their action as "good". However, the rest of the world, including droves of Muslims, condemn the teachings because they can see they are destructive, and serve no purpose to humanity or it's advancement.