One thing I personally like about HN is that, in general, I can read the comment and form an opinion about it before I read who posted it. If the username was 'in your face' it would be harder to not let that colour your reading.
For example, there are several prominent members here who post very reasonable and thoughtful comments that I often agree with, but sometimes disagree with. I think it would be harder to judge their comment on its merits alone if it was very visible that it was <prominent user> who posted it.
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One thing I personally like about HN is that, in general, I can read the comment and form an opinion about it before I read who posted it. If the username was 'in your face' it would be harder to not let that colour your reading.
For example, there are several prominent members here who post very reasonable and thoughtful comments that I often agree with, but sometimes disagree with. I think it would be harder to judge their comment on its merits alone if it was very visible that it was <prominent user> who posted it.