They kill us because they quite literally have not a single clue as to what is going on. One second they're minding their own business trying to manage day to day existence on this planet and a helicopter full of Marines shows up and starts killing everything. Destroying their homes, killing the livestock they desperately need to survive, etc. But why? Well they don't know. They have not even the slightest clue as to why we are in their country, or why we hunt the Taliban. And it angers them and pushes some of them to the breaking point.