I actually think this would encourage more thoughtful rebuttals in the form of long blog posts. One great thing about this community is that usually there are enough people to promote stories on opposite sides of the debate to the front page.
The assumption here is that blog post followups to popular front-page stories will themselves naturally find the top of the front page. But of course they won't. For one thing: simple causality guarantees that they won't be available until hours or (depending on the quality of the post) days after the original story first hits the front page, when it's at the zenith of its gravitational pull for HN votes.
