For those who are unaware, particularly unloved questions are [automatically deleted](http://meta.stackexchange.com/a/92006).

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](https://physics.meta.stackexchange.com/a/6003/51994).