If we follow the logic of Yishan's thread, HN frowns upon and largely doesn't allow discussion that would fall into group 3 which removes most of the grounds for accusations of political and other biases in the moderation. As Yishan says, no one really cares about banning groups 1 and 2, so no one objects to when that is done here.

Plus scale is a huge factor. Automated moderation can have its problems. Human moderation is expensive and hard to keep consistent if there are large teams of individuals that can't coordinate on everything. HN's size and its lack of desire for profit allow for a very small human moderation team that leads to consistency because it is always the same people making the decisions.