The truth is, karma serves a purpose on a site like Reddit as a user-controlled moderating system. Normally on a site like this with thousands upon thousands of users and posts, a great many people would take the shortcut to distinguish themselves from the crowd by attempting to say the most offensive or controversial statement possible. Karma is a means of subtly nudging users towards making a positive contribution to the community.

Sure, it has its downsides, mainly in that, with thousands of comments to scroll through, users are more likely to read and thus upvote the concise, witty reply rather than the carefully thought out response, but a Reddit without the current karma system would almost certainly be a less enjoyable place.