Killing somebody needs great effort. Killing somebody secretly requires even greater effort. In addition killing involves large risk of getting killed instead.

Killing somebody needs great effort. Killing somebody secretly requires even greater effort. In addition killing involves large risk of getting killed instead. The risk increases when this practice becomes more common. It is simply easier and considerably less risky not do something like this. But there still exists people who argue similarly to your ideas and act based on them. These people are called murderous psychopaths.