Mark Perakh, writing at Talk Reason, quotes Dembski from one of a series of Sunday lectures he gave in a church. Dembski's own words about what motivates him:
"I think at a fundamental level, in terms of what drives me in this is that I think God's glory is being robbed by these naturalistic approaches to biological evolution, creation, the origin of the world, the origin of biological complexity and diversity. When you are attributing the wonders of nature to these mindless material mechanisms, God's glory is getting robbed." He continued, "And so there is a cultural war here. Ultimately I want to see God get the credit for what he's done -- and he's not getting it."
Thanks to Ed Brayton for this link. I think that it is important to keep in mind that people like Dembski are motivated by religious zeal rather than simply a desire for scientific understanding about the world.
This is not, as you can tell, even a matter of someone simply looking to better understand "God's creation," which would not by itself be a problem. Instead, we are looking a people who are motivated by a desire to push a particular image of a particular god throughout American culture - and their platform of choice is science rather than politics or an honest pulpit.