As opposed to tearing through a thread and downvoting any and everything you disagree with.
Slashdot encouraged more positive moderation, unless you were obviously trolling.
The meta-moderators kept any moderation abuse in check.
It's sad to see we have devolved from this model, and conversations have become far more toxic and polarized as a direct result of it. (Dissenting opinions are quickly hidden, and those that reinforce existing norms bubble to the top.)
I believe HN papers over these problems by relying on a lot of manual hand-moderation and curation which sounds very labor intensive, whereas Slashdot was deliberately hands-off and left the power to the people.