Most Darwinians are theists. The theory of evolution has religious implications in that it disallows literal readings of the Bible and Koran, but then so does much of physics, geology, astronomy, etc.. Simply because a religion makes highly implausible statements about the state of or history of the world, does not mean that any science that contradicts those statements is intrisically religious.
And here's where your logic comes full circle. You start off with the assumption that ID is highly implausible, and then use that to "prove" that the people who adhere to it could only do so for religious reasons, and then use that to bolster your view that the theory is implausible, because it's only being supported for religious reasons.