Because hot, flamey, sensational threads are the cheetos of the internet, and if we didn't downweight them they would take over the site and make it a different kind of forum.
On HN we're optimizing for one thing: intellectual curiosity [1, 2]. That means encouraging threads that satisfy that quality, but it also means weeding out most threads that don't satisfy that quality. Most riler-uppers [3] don't. That doesn't mean they aren't important. They have other qualities, just not the one we're optimizing for.
Although this moderation strategy follows from the first principle of the site, it has many tricky aspects. Sometimes there are stories that have both qualities: intellectual interesting as well as rage-inducing or polarizing [4]. In those cases we tend to go by whether the community is able to have a discussion that at least doesn't burst completely into flames. We also consider whether the general topic has been discussed recently, since curiosity withers under repetition.
Sometimes there are stories that don't really gratify intellectual curiosity, but contain such important news that users will submit them over and over again regardless of how much we downweight them. In that case we yield to the community and try, if possible, to consolidate the discussion of that story into one major thread. After that, we downweight reposts until there is significant new information [5].
This StackOverflow story seems to fall somewhere in the overlapping circles of that Venn diagram; it's not devoid of intellectual curiosity (rapidly changing social/political conditions; internet community management; etc.), and it's also something the community seemed determined to discuss (to judge by how often it kept getting reposted). That gave it enough energy to hop into a different orbit than your typical yet-another-angry-dispute would achieve under routine HN moderation.
> Got me thinking wow, some people really don’t want anyone discussing this topic! I wonder why.
When people hear about story X getting moderated, if story X is something they care about, it immediately feels like story X is being singled out for suppression. Then the question arises: why are you censoring X? If you only ask that question about X, it always seems arbitrary and unfair.
From a moderation point of view, though, nothing is singled out—the strategy is systematic. We're basically like snow-ploughs or street-sweeping trucks that do their job every day to clear the roads. If we didn't, the roads would pile up with snow and/or trash, i.e. the site couldn't function as intended. There's never a particular intention to suppress a particular story—on the contrary, to the extent that a story gets particular attention, it's usually to decide whether a penalty should be waived, as in this case.
If you want to understand HN moderation, you need to understand that all this takes place at scale. We make moderation calls like this dozens if not hundreds of times a day, mostly via pattern-matching and heuristics (including in software, when we can figure out how to write code to do it), because there isn't time to do it any other way. Invariably, we guess wrong in many cases, not because the strategy is wrong, but because no systematic strategy can bat 100. Plus there will always be borderline calls, which by definition are arbitrary.
If you still have questions that aren't answered by the above, I'd be interested in hearing what they are.
1. https://news.ycombinator.com/newsguidelines.html
2. https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
3. https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
4. https://news.ycombinator.com/item?id=17014869
5. https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...