In practice, pretty much any topic where people can remain civil is generally ok.
I'm aware commenting on moderation/appropriateness of submission is also outside of guidelines, but I think given the gravity of this event and the clear slant evident in top comments resultant from the difficulty of moderation "crap comments" it does seem worth mentioning that this doesn't feel like it belongs here in the HN community.
Statement of my own biases: from a country that suffered the horrific hand of British colonial forces, both preceding and under Elizabeth's rule and finding the comments here repulsive. Positivity can be just as "crap" as ad hominem when expressed with such ignorance.