Earlier quoted context omitted.
Maybe a dumb question, but how can you brigade against on Hacker News if there is no downvote of submissions?
When you get enough karma, you can "flag" submissions. If enough people flag a submission, it gets buried and won't show up on the front page anymore.
But maybe even some light flagging, plus high engagement-to-view ratio (esp. if engagements go many levels deep fast), may cause some "unwanted" content to be buried.