Honest question, why is
this post a bannable offense?
What am I missing?
My guess is that there was a sweep of that thread for thread whining (i.e. I do not think this should be a thread so I'm replying to complain that it is). A marginal case to be sure, which is why it was a short ban, and it might have went under the radar if a bunch of people didn't pull the same crap, but we live in the world we live in. In particular, it is common for people with regressive social views to enter any thread on social issues to complain about it "not being a big deal", "people overthinking it", etc.
In the terms of service, that particular thing is listed under "Do not post disingenuously, or in an inflammatory manner for the sole purpose of upsetting others... Negative commentary and minority opinions are not frowned upon, but members are expected to be able to substantiate their positions. At the same time, do not derail threads around yourself". In the FAQ forum,
we elucidate further on some of the kinds of things we categorize as whining about the thread.
Finally, I'd note that most bans take into account context (i.e. has this user been posting consistently bad or borderline posts for a while before that, do they have a past record of doing this exact thing, does this seem like a good poster having a cranky day or like someone whose ice is getting thin) -- which is one of the reasons that typically a ban is between the banned user and the moderation and why we don't make ban messages public. In this particular case, the situation seemed to warrant the public disclosure precisely because the user characterized his record on these things in what I would consider to be at a minimum a misleading way when he was correctly called out for it.