The Law of Karma is quite mathematical in its precision - we are always receiving exactly what we deserve.
It makes sense, to believe that we earn what we get and where we go, whether it's applied to just this life, or into others both past and future. I mean, even Christians believe (preach) the Golden Rule, and most everyone believes the adage that says, "What goes around comes around."
Hell, the Christians can't even really argue with the idea of Karma, the way I see it. If Karma works on the principle that you must give in order to receive, and there is some mathematical equation to it, what difference is there between Karma and the idea of the tithing 10% that the Christians adhere to so faithfully?
What bothers me about this whole discussion is that my arguments seem to be aligning me more closely with some of the Christian beliefs than I like to see, which sits like a rock in my gut and burns at my throat a bad case of reflux.