It is not a miscarriage of justice, because the justice system is working as it is currently written and interpreted in this situation. If you're interested in changing the laws (or the protestors are), then it would be productive to work with people in the legislative branch, our representatives, and with people in the justice system who could suggest modifications.
I'm sure there are people who beat their children to within an inch of their lives and get out on bail - are these protestors diligently seeking them out for their next big protest? Are they advocates of the cause of children or are they simply very angry people fed up with the A's, especially Casey? I would have more respect for the former; the latter seem to me to be more like the mob mentality that our justice system is supposed to help us avoid (vengeance attacks, for example).
I understand being fed up -- I'm sick and tired of the A's when they speak to the cameras, and I don't think they are what is right by their granddaughter -- but I also think there are more productive ways to go about expressing this or dealing with this anger than standing on the very edge of the A's property screaming; I think there are better places to protest or try to get action so that this situation doesn't happen again (if one really believes it's unjust generally); and frankly, I think there are better ways to be a citizen in a democracy. Peaceable protest and assembly are allowed, but just because it's allowed doesn't always mean it's the best choice in the situation. This seems to be feeding the morbid spectacle and not the cause for justice.
We are all impatient for this case to move forward, but the justice system is moving at its own pace -- standing outside screaming at the A's and provoking confrontations will not make it move one iota faster, nor will watching it on the webcam almost hoping that something violent happens so that the grandparents of Caylee can get in trouble. That does not seem a productive way of dealing with frustration with them to me. It won't help Caylee's case, and she should be our main focus.