Initial thoughts are that the people defending this are simply naive, but then you realize that white people just have no idea what racism is like. They might read some stories, but their first reaction is to usually get defensive and try to label it as something else like "stereotyping". "It's not wrong if everyone feels the same way about those blackies, right?" :confused
Half-whites can be just as racist as full whites, so I don't understand that argument. The main issue here is that the police told Zimmerman not to pursue, and he still went against their instructions and chased after the child. It's not illegal to walk through a neighborhood with Skittles, an iced tea, and a hoodie. It IS illegal to commit battery/assault and manslaughter. It's also morally wrong to assault a child where I'm from at least.
The child defended himself, and got shot for actually kicking the dude's ass while being attacked. I was taught to defend myself, and I sure as hell will teach my children too also.
The police (white), and lots of other white people see nothing wrong here. That's an inherent issue, because this would not have even occurred if the same child were white. And if it did, then they would have actually investigated thoroughly at the time and Zimmerman would be in jail right now awaiting trial.
Race has lots to do with it. The media might blow things out of proportion, but the FBI and Justice Department don't just casually get involved in cases.