The mouseover tooltip for Question downvotes says This question does not show any research effort; it is unclear or not useful (the one for Answers just says This answer is not useful). Browsing the FAQ, I can't find any additional guidance.
For reasons that continue to elude me, Downvoting questions because you don't want to answer it was closed as Not Constructive. I appreciate the question title was misleading (it misrepresented a stated position of mine), but personally I never understood whether the downvotes to that meta question represented people disagreeing with the OP for questioning my (actual or misrepresented) position, or people disagreeing with my (again, actual or misrepresented) position.
Obviously we don't all agree on the precise justification for Question downvotes (if we did, anything with more than a couple of downvotes would probably end up several hundred down!).
My proposition is that I think the FAQ should offer more guidance. I'd prefer this question be up/downvoted strictly on that proposition, not on my personal attitude to Question downvotes.
One specific position I do hold (but please don't up/downvote on this - just the proposition above) is that I think the FAQ should at the very least mention that ideally, we'd like downvoters to add a comment explaining their reason in more detail (obviously it's not a requirement, but for me at least, something like recommendation sounds plausible).