At what point does it pass from humour to offensive content?
I guess the point here is that there is no definitive answer to this question because what is considered humorous or offensive is subjective.
We do get questions and answers which are clearly spam or offensive and I have found that, on Puzzling SE, moderator intervention is efficient and appreciated by the vast majority of the community on these occasions.
However, it sometimes happens that a user has written a question or answer that, unintentionally, may be considered offensive by another user on this site but maybe the poster, and others, have not considered that particular perspective.
What I would like to see, when this happens, is an open discussion between those involved to consider a rewrite of the question to the satisfaction of everyone.
I think the linked question provides a good example.
For me, this question did not spark any notion that the asker was being intentionally provocative.
However, I do understand the moderator point that the idea of "black squares matter" may be seen as trivialising the "Black Lives Matter" movement.
What I would like to have seen in this circumstance is an initial comment under the question along the lines of
"The way you've made the connection to the 'Black Lives Matter' movement will be interpreted by some as trivialising what is a very important movement. Is there any other creative way you could rewrite the question so as not to do this?"
I think the OP would have been open to this because, as puzzlers, most of us like being creative.
What I think is not helpful is considering bad intent from the other side when it might not be there because it will inevitably create ill feelings on both sides (and lead to messy edit wars, etc) and you may get a splurge of comments underneath the question/answer debating the issue one way or the other.
I do think the moderators are doing a great job on this site and I find Puzzling Stack Exchange a fun place to visit regularly because there are so many interesting and creative questions. I wouldn't like others to feel like they can't have fun here and while this means being mindful about how we phrase questions and answers, it should also be considered when we approach resolving these issues.