"All they have to prove is that they fear for their life. It does not have to make sense, does not have to be 'justified', etc."

That's not really true. The standard is a reasonable fear for your life. That's reasonable standard is evaluated in court by how a reasonable person would have reacted. Yes, they do give some deference to the individual who was actually there (police or civilian). The real problems happen because the DA and the courts tend to have bias when it comes to subjecting members of the system to the same process that others face.