From one of my favorite movies: Sgt. York, staring Gary Cooper, based on the true life story of Alvin York. The end of the first clip shows Sgt. York using his excellent sniper skills, to pick off Germans one by one in World War I.
The reason why we can be against murder and yet also be for self-defense of the helpless, a just war and capital punishment (Genesis 9:6; Romans 13:1-8), the second Amendment, and understand the need for the proper use of guns - to kill the bad guys.