The only rational conclusion, based upon the evidence that I've seen, is that Officer Wilson should have been indicted, and then probably found not guilty. I personally suspect that he committed murder - probably he drew his gun prior to any violence, Brown reacted to defend himself, and got murdered. But the evidence isn't there to prove it, so he'd have to be released, which is unfortunate, but the only fair way of doing things.
The reason why it is important to follow that process is because the process is important in and of itself. It is how political and legal legitimacy is maintained. If you simply throw away these processes, what you are going to see is continued deterioration of policing and law & order.