That perception usually seems to be more related to the strength of one's own ideological commitment than to the actual state of the threads. People on each side perceive the community to be biased, and people who are intensely on one side perceive the community to be extremely biased.
i'm not going to do a study of the culture of hn because i am not an anthropologist but i have many times responded to comments that were vile, that broke the rules, that did not get flagged because they toed the party line, that were in effect supported by the community
is obvious. what is insidious is the ideology that is preached on almost every controversial thread that papers over that fact.