I don't quite think those comments are meant to be amusing, it rather profits from the division (into likers vs. non-likers) that has already happened. Post a similar comment on Rebecca Black's "Friday" music video (which has far more dislikes than likes), such as, maybe, "10 people are looking forward to the weekend, 30000 enjoy mondays more", and your comment will - this does my hypothesis predict - be voted down, even though they might be as amusing as other, similar comments.

I agree that they profit from the division between likers and dislikers. But I think the amusement comes from finding a creative way to insult a minority. If any of that sort of comment are on the Friday video, I predict they will be making fun of the minority of likers.

I have encountered quite a lot of [gruesome details] spam a few years ago, and back then, when I was still younger, those did make me nervous, although I knew it was BS. I think those comments are now regularly marked as spam, downvoted and deleted, but simply the fact that they are downvoted shows that people don't find them amusing, doesn't it?

The fact that they are spread shows that some people are either amused or nervous. The fact that they are downvoted shows that other people are both unamused and not nervous. I expect that the population of people who encounter them is split, with some proportion amused, some proportion nervous, and some proportion neither. Our question depends on the relative sizes of the first two factions.