What about reserving the pending system for stories on the front page where you typically get the bulk of low-quality comments? A user commenting on a 2-day-old front-paged thread is either contributing meaningfully or feeding a flamewar, so by automatically endorsing all comments on stories that have fallen off the front page, you allow the former to continue a meaningful discussion unhindered and you give the latter no incentive to continue a meaningless argument (no one is seeing it).
Also, from what I've noticed, the Ask HN posts tend to receive comments of higher quality since the questions/submissions there aren't as sensationalist or polarizing, yet that particular section of the site receives only a fraction of the attention that the front page gets, so implementing the pending system there might unnecessarily stifle discourse.
Also, from what I've noticed, the Ask HN posts tend to receive comments of higher quality since the questions/submissions there aren't as sensationalist or polarizing, yet that particular section of the site receives only a fraction of the attention that the front page gets, so implementing the pending system there might unnecessarily stifle discourse.