Not just any karma, in game karma Points.
You see, I can see this being beneficial as well.
If playerA helps PlayerB and gets Karma Points for it, PlayerA can save up a bunch of these karma points and PlayerC who checks PlayerA's Karma Points can see how helpful he is to the community and others and will concider helping PlayerA when PlayerA may need some help for his own thing.
am I right?
But still, I prefer reward system over all since I like to obtain gil/exp or anything worth while durring helping friends out. Not everyone enjoys putting time helping others for nothing. But everyone loves to get things from helping so OP's idea is to help community help each other better for each other since everyone gets worth while rewards who participate which I am all up for that.