Part of that though is that +1 Funny doesn't add to your slashdot karma. So people sometimes "upvote to denigrate" because you can only get +5 anyway, a silly comment can get +5 Funny without actually rewarding the commenter (mocks the comment) - you can see this when replies get +5 Insightful or +5 Informative and are very contrary to the original comment.

Personally, I like the idea of having qualifiers on the downvote without one on the upvote - makes you think a little bit before downvoting... plus the vote buttons are ridiculously small on an mobile Safari - so having to click twice would prevent accidental downvotes.