The point of these shirts is to show how silly the whole ID "Teach the Controversy" argument is because, unlike the Theory of Evolution, there's nothing scientific about it. Thus, ID is in the same league as the "Space Aliens built the Pyramids" theory and the "World is on the backs of four elephants, who are in turn supported by a giant space turtle" theory. I doubt that Christians would want ID placed alongside such theories as these, but they all share the commonality of having no scientific validity.
The problem here is with the top center design above. If you can't make it out, it's a picture of the Devil (in work overalls, no less) shoveling dirt onto some dinosaur bones. Most supporters of Intelligent Design would disapprove of all these designs ... except for that one. For them, the theory that Satan planted dinosaur bones in the earth so as to sew doubt in the minds of believers is completely plausible. It shares the unscientific nature with the others presented but, unlike the others, some Christians would have little problem with it.
So basically, you might very well find Christians wearing that top middle design without any humorous intent. Which makes me wonder if the manufacturers were cunning enough to actually plan that.