I've never liked karma systems.
On the surface it seems to make sense: People who are helpful/insightful get lots of karma.
In practice, it fails on two fronts:
First, karma systems in and of themselves work based on popularity, under the mistaken idea that popularity = correctness/insightfulness/suitability. Quite often, the most insightful or thought provoking ideas are unpopular (or speaking the truth is unpopular). What you get is a system that automatically filters out the ideas that the majority are unconfortable with, and so you end up with an echo chamber which doesn't admit new ideas.
Second, the policies formed around the karma system grow biased AGAINST new users over time, which leads to community stagnation:
The initial couple of years are great. The early adopters are all eager to participate in meaningful ways, and build a thriving, vibrant community.
Then the gamers join in. They learn how to game the system to gain points. They do this just to show that they can.
Closely related, the karma whores move in. Their sole goal is to gain points for self-worth. The community is meaningless; points are everything.
As the gamer's techniques become more widly known, the spammers move in, automating the techniques to promote their spam, and the cat-and-mouse game begins, usually at the expense of making things more difficult for the users. These measures are almost always done with consideration of the already established user base, using them to determine what a "normal, real" user is like.
Once you hit this point, it starts to become prohibitively expensive for a new user to join in, thanks to the biased notion of a "normal user". Stack Overflow is a prime example of this, where you have to jump through all sorts of crazy hoops just to be able to even comment or gasp edit your own question because upon re-reading, you decide it's not as clear as it could be.
And so you complain. But people don't like complainers, so they all jump on you and say "It's not so bad! I went through the red tape and so should you!" and "If you don't like the red tape, there's no place for you here!"
There's a word for this: Bureaucracy.
As a service provider, you should be doing everything in your power to make things MORE accessible to new users, not LESS accessible. You should be ENCOURAGING participation, not throwing hurdles in their way. New users are fickle. Their first experience on your site will largely shape their perception of it forever. Start them off with a bad experience and they'll refuse to participate. Rampant bureaucracy is a sign of severe failure in the system.