Back in the day facebook only had a like button and people demanded a dislike button. I don't know what facebook thought internally.
I think what kbin really needs is reasons. (like slashdot - though I havne't been there in 20 years so I don't know what is current). Upvote because it is funny is different from upvote because it is insightful (I may want to filter on that). Downvote because it is SPAM vs downvote because it is insightful on how someone who is wrong thinks (which probably should count as an upvote) Of couscous I don't know what the fedration protocol allows.