You should do some research to get the whole story. Brown was going after the officer's gun. The officer's action was lawful and saved his own life. Zimmerman actions saved him from great bodily harm or death.
What you don't understand is that we, and that includes you, have the right to use any and all force, up to and including lethal force to prevent great bodily harm and death. It has nothing to do with what race or sex of the violent offender is as the democrats want you to beleive.
People against self defense have never been a victim. Being a victim of a violent criminal can change a persons views and beliefs pretty quick.