I think Facebook and this forum are quite different: I like/d that one couldn't simply downvote a post and move on if they didn't agree, they had to actually articulate a reply. The smaller community and good moderation makes nixers feel friendlier.

The topics of nixers are all niche and closely related anyway, and there's sometimes overlap between categories which makes them less helpful or confusing.

Obviously we can differ here, but I see nixers as a category in itself, so it doesn't need subcategories.