I think this is one of HNs biggest weaknesses. If you are a sufficiently large engineering organization with enough employees that pass the self-moderation karma thresholds, you can essentially strike down any significantly critical discussion.
Without a public moderation log (i.e. even user flags being part of the log) claims like this will always come up but to me it always seems more likely just the early commenting users tired of being told they are part of some astroturf campaign and if they don't flock to agree with the OPs views it must just be more proof.
I'm sure both reasons happen to some degree, just as a matter of how often is actual astroturfing vs "a small percentage of active people can't possibly just have different thoughts than me".
I think this is one of HNs biggest weaknesses. If you are a sufficiently large engineering organization with enough employees that pass the self-moderation karma thresholds, you can essentially strike down any significantly critical discussion.