(Although you may not think so and therein lies the beauty of it)
If there is objective truth, then why can't people agree on anything? Well, because if there is objective truth (and this is what it would be: not value judgments, but the simple state of things), there is no way we can access it. We cannot know it and know that we know it. If we happen to believe correctly, then there is no means of verification. We are a product of our environment. There is culture, there is perspective, there are different moral codes and structures - each with their own pros and cons. But the pros and cons are subjective - and that is why we disagree. We cannot make an objective value judgment. The very natures of the words 'value and 'judgment' are relative.
Objective truth, as the simple state of things, is free of 'value', free of 'judgment' and dependent only upon its own solidity - not our validation.
To point out that I have my own moral code does not defeat my argument. Relativism does not deny a moral code, simply a universal one. You ask me a question, I can give you my answer, but I can give you only mine. I cannot speak with the voice of the world, or the voice of truth with a capital T; I can only speak with the voice of my own personal perspective.
If there were objective truth, if we could all know it, we would at least have a chance at agreement. but as things stand, we do not. There is not only one right and one wrong in every situation. Even if there were, I would not trust the church to be the judge of it. I see no clearer understanding of morality in Christianity than anywhere else - just more legalism.
And that is why I am a relativist.