"So in your opinion we can never improve because when we try to improve ourselves to not be prejudice, the more prejudice we become?"
No. That is not my opinion. I did not say that, and can not imagine why you would think that.

"So what is the use of trying? We might as well admit that we all harbor prejudices and just live with them."
That seems rather cynical.

"That is like saying that since as a Christian I know that I am a sinner, therefore since I can not live above being a sinner, I might as well act like a sinner and not try to be a better Christian. Is that the idea? "
No, not at all. Perfection, though unattainable, is certainly something we should always strive for.
I would love to continue this discussion with you, but unless we can get this back onto the Civil War, we need to drop it. Why don't I just acknowledge that you're a much better person than I am (that should make you feel better, and it won't bother me a bit), and we let this whole thing go?