So, basically you want to start another popularity contest that will have no effect on people's posts. Hence, not doing any form of moderation. Most likely be used with those with "good karma" to hold over the head of those with "bad karma." Very similar to the "Like" feature. In a sense, another area for people to troll others in...

Have no idea what this would do with trolls. Might as well take the wiki approach and let everyone moderate everyone else.....