Some titles/subtitles I'm thinking about: "History of HN", "Introduction to HN", "Who are the users?",... Can you please give me some topics I should touch in my essay?
See: Snowden, Bitcoin, etc.
If it is the former, then "History of HN" and "Introduction to HN" would make terrible topics for an essay.
My understanding is that most teachers look for your ability to persuade, typically using a standard five-paragraph essay format. The key to this is selecting a good thesis. Typically, I prefer to select a thesis that reflects the opposite of my personal viewpoint (e.g. if I believe that students should spend more time on Facebook, then I typically like to write essays arguing why students should spend less time on Facebook). The reason I do this is two-fold. First, by researching the opposing opinion, it helps me formulate how I would actually argue against it if I ever needed to in a real-world situation. Second, because I believe the opposite of the thesis in my essay, I'll always remember to include remarks acknowledging the viewpoint opposite the thesis, which makes the argument more palatable for the reader. ("Oh, hey, at least he considered my side.")
In particular, facts make for a terrible thesis, because there's no reason to argue the other side. A good thesis considers an issue that can be argued both ways.
I would characterize it as a combination of nitpickiness, the need to articulate the "Right Answer"[1], and of course a desire to show off one's knowledge, that often results in interesting discussions full of counterpoints and analysis, but also can lead to flame wars full of righteous fury and petty snark.
1: e.g. http://xkcd.com/386/