However ridiculous creationism or conspiracy theories may be, it's still useful to have a clear explanation of why they are ridiculous, if only for the sake of anyone who's not completely up to date on the topic. For the other example you named, creationism, even if creationism is extremely silly it's still useful to have a summary of why evolution is more reasonable.

For myself, i can say that i'm not a conspiracy theorist, but i haven't really researched this topic, so i don't have a justification for "why 'WTC explosives: no' is a slam-dunk" off the top of my head. So, the discussion resulting from PlaidX's initial question has raised at least one good point that i hadn't thought of before.