A friend posted this after watching the debate between Ken Ham and Bill Nye. I think it basically sums up why these debates are pointless:
"Mr. Ham wants it both ways. But trying to find scientific evidence to prove something God requires you to take on faith is a fruitless pursuit. Faith doesn't require evidence, that's why it's faith. This debate can't really go anywhere because evidence can't affect Ken's beliefs and Bill can't accept Ken's beliefs without evidence."
The above may seem obvious, yet these debates continue. However, I assume that Bill accepted the debate to hopefully influence a few of the creationists in the room and watching. If anything, he got them thinking about the irony of their position, not the other way around.