There are two levels to answering questions like this. The purely mechanical is that enough HN members clicked the "flag" link to cross the "[flagged]" tag threshold. The second level answer is to speculate why those members chose to click "flag". That's tougher, though in my experience one of the reasons is because some members observe that unfortunately some topics are difficult to constructively discuss on HN, regardless of the importance of the topic. I think the current discussion is a pretty good example of that, in generating more heat than light. Note that this doesn't mean these topics shouldn't be discussed, just that there are likely better places (both online and off) to do so.