You might want to add a question: + Why can't I downvote comment? with the answer + You can only downvote comments once you have sufficient karma. The requi

You might want to add a question: + Why can't I downvote comment? with the answer + You can only downvote comments once you have sufficient karma. The required level rises over time to account for the karma inflation caused by an increasing userbase. This would enhance the answer about what one can do with one's karma.