For those who are unaware, particularly unloved questions are automatically deleted.
A question with a -1 score or lower and no answers gets deleted in 30 days.
A question that is closed (not as duplicate), has no answers with score >0 (or accepted) and has not been edited in 9 days is deleted after 9 days.
So, in terms of keeping the site clean, for a majority of the types of questions we are talking about, the difference is getting it deleted only 21 days sooner if we vote to close rather than downvote.
I don't think that is enough of a benefit to argue against the intrinsic subjectivity that Jim mentions.