I don't know the specifics of this, but vouching "against" the hive mind leads to your vouches not doing anything any more. I assume that either there's some kind of threshold after which you're shadowbanned from vouching or perhaps there's a kind of vouch weight and "correctly" vouching (comment is not re-flagged) increases it, while wrongly vouching (comment remains flagged or is re-flagged) decreases your weight.
We sometimes take vouching privileges away from accounts that repeatedly vouch for comments that are bad for HN in the sense that they break the site guidelines. That's necessary in order for the system to function—you wouldn't believe some of the trollish and/or abusive stuff that some people vouch for. (Not to mention the usual tricks of using multiple accounts, etc.) But it's nothing to do with the hive mind and it isn't done by the software.
