“Not what I want on HN” ≠ “I am offended”

Among other things, it can mean, “dear God, just from the title I can tell that the comments on this are going to be 90% people staying their preconceptions of how other people will feel about it and/or imputing motives to thread or comment moderation, 5% people reacting to the title, and 5% people quoting the article in response to the previous 5%.”

If it's not what the want on HN they can ignore it. The flag button is used as "stuff I don't want anyone discussing or knowing about".