There is no reason, based on the HN guidelines, that the referenced post should have been downvoted, let alone flagged. Whoever did so abused their power to make such decisions.
It's even more surprising since HN had the "vouch" feature since before Dec. 2016 [0]. My best guess is that people might have reflexively downvoted/flagged upon seeing the opening sentence of "Black people are measurably less likely to own a car or have a bank account".
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[0] - Not sure what's the power of a vouch relative to a flag or a downvote, but my impression is that it's stronger.
I'm coming to the opinion that downvoting should not grey out posts, or that there should be some number of downvotes (greater than 1) required before it starts. It should be harder to suppress constructive, on-topic posts just because a bunch of people don't like the point.
This "drive by down-voting" happens regularly here. I've had comments downvoted within seconds of posting--clearly the voters could not have had time to read the entire text. They see a few key words that trigger them, hit the arrow, and move on to the next job. Unfortunately, there's no way in JavaScript to tell whether someone's actually read the thing they're down-voting, so we get these knee-jerk keyword-based brigades.
To test this, sometimes I'll write something where the first sentence is provocative, but the rest is (I hope) a solid, nuanced argument. Usually it's at -1 or -2 within a minute, and then over the next few hours slowly crawls back up to +2 or +3 as people actually read it.
I cannot but confirm this behaviour.
Also I noticed that (my guess is that there is some form of subliminal self-defense reflex by some categories) there are a few themes (not political, not social) that seem to attract downvotes.