I think one thing that's being overlooked is that a lot of people (or maybe just me, but I like to think I have somewhat common thoughts) aren't really upset by the verdict but by the case. And in this, Zimmerman is actually just, fairly or not, a personification of wider issues in America today, issues that some seem to be willfully ignorant of.
I asked about the racial overtones being used by some of GZ's defenders because it gets to the core of the issue: there is a still-present double standard in American society and it's institutional. I'm not saying that Zimmerman himself is a racist (biased, sure, but who isn't?) but rather, this case came to encapsulate everything unfair about American society to many people. So, again in fair or not, Zimmerman's acquittal was symbolic.
I question if many white Americans have ever actually wondered what life is like for black men. While you might think opportunities are the same, do you really think the experience is the same? I'm going to paraphrase a cousin of mine on this:
You're not allowed to get angry. If you get angry, you come across as scary. You have to be conscious about how you're being perceived, because you're held to a different standard.
That's the racial side of this. It's not that Zimmerman wants to be a Klan member, but it's that Zimmerman likely made a not-too-uncommon judgement about a dark-skinned kid in his neighbourhood. Trayvon's death is just a stark reminder that, yeah, you best do your best to look less threatening.
It doesn't help when his brother calls Trayvon a gun-running dope fiend and asks why blacks are so violent. It doesn't help when his lawyer makes a crass remark that had Zimmerman been black, this wouldn't've made it to trial (I don't care if it's true, it was a crass thing to say).
The second factor is the institutionalized nature of disenfranchisement. There was a quote earlier in this thread that I really liked:
The justice system worked. Miami Marlins outfielder Bryan Petersen said it best, "If you trusted the justice system to find a man guilty, you must trust it when it finds a man not guilty, or it's just partiality you seek." That pretty much sums it up for me.
but it misses the point that many blacks in America don't trust the justice system to find a man guilty in the first place. The justice system, not through nefarious design (or so I hope) does screw over blacks disproportionately, regardless of the crime rate between blacks and whites: more likely to be arrested, more likely to face more serious charges, more likely to be poor and rely on public defenders.
Again, Zimmerman isn't responsible for any of this, but he became the face of it. It might not have been fair, but that's where a lot of disappointment stems from. Zimmerman might not have been guilty, but the system is seriously screwed up and it's not being addressed.