I'm not sure whether karma is a comforting thought or a frightening one, considering all that we do in our lives. Who knows what the effects of all those deeds might be?
My DH's family are devout Hindus. He is an atheist who goes along with the rituals at weddings and funerals to keep his family happy. At a service held a week after his father's funeral, the priest rambled on for ages and, at one point, said that my FiL would be born again in fortunate circumstances because he had been a good man in this life. (That's a matter of opinion!) Those who had been bad would be reborn to suffer, such as those now living in Darfur.
It struck me, not for the first time, that the doctrine of karma could be misused to blame the victims. It can certainly make the rich feel entitled and under no obligation to help the poor, who had brought it on themselves. I thought that it was particularly hard on the people of Darfur! My husband felt the same and whispered in my ear, "What a load of bullshit."
I should add that, from what I have read, I think that the doctrine of karma is more subtle than that. I did think that a priest would manage something a bit more nuanced than the idea that victims of genocide had been bad in a previous life. On the other hand, Christianity claims that, on the basis of one life, you are going to heaven or hell for eternity. That's not very nuanced either.