I think Justice exists and is more than just morality. I think it creates a desire in each of us to exist in a sense of equilibrium or rightness, because when that equilibrium is missing we feel ill at ease. As a clumsy metaphor, when we're cold we try to find ways to make ourselves warm. With Justice, when we're wronged, we try to find ways to rectify that.

I also happen to think of Justice in terms of a moral absolute that is beyond our perception. In the sense that there is an absolute right and an absolute wrong. Where we struggle comes from the fact that even though it's binary, it's so grainular that in many areas all we see is grey. Partly because the distinctions can be so elusive, but also partly because we don't always have the proper insight.

I think our changing perceptions of what is right and Just has nothing to do with any fluidity of Justice and everything to do with our abilities to see things in better and clearer detail. Justice for us today, in terms of laws for example, might be very different from Justice five hundred years ago, not because Justice changed but because our understanding of ourselves and the world around us has changed.

I'm religious, so that colors my ideas a bit, but I think even in a secular way the above makes some sense.