Because you have never had any formal training on the laws governing use of force, and your worldview is shaped by the opinions of people who have never had any formal training on the laws governing use of force. Unfortunately, with a few rare exceptions (Chris Dorner, Philando Castile spring to mind) the deceased also had no formal training on the laws governing use of force.

Dorner knew them, and committed suicide by cop. Castile knew them, followed them, and was murdered.

It is a travesty that our government only provides this training to police. It should be taught in high-school civics/social studies/government classes, so the general public is aware of when it can use force, and when force may be used on it.