Because it establishes Martin's intent in the situation, justifies Zimmerman's response to Martian's presence and also sheds light on whether or not lethal force was is only recourse.
Okay? But given the history in the neighborhood and the Cop's inability to prevent it, maybe relying on them wasn't an option. Who's to say Zimmerman didn't stop a rape that night? Didn't you say once you would have shot the people flying the planes on 9/11 before they committed the act because you knew they were about to commit it?
How is Zimmerman doing what he thought was right, stopping a potential robbery, really any different other than scale of crime?
This is bullshit and you know it. You can't, repeat, cannot, haul off and physically attack someone because they ask you why you are in their neighborhood. Yell and scream back? Sure, but physical assault? Nope.