From the scientific view, the theory of karma may be a metaphysical assumption -- but it is no more so than the assumption that all of life is material and originated out of pure chance
Unless you see your nature, you shouldn't go around criticizing the goodness of others. There's no advantage in deceiving yourself. Good and bad are distinct. Cause and effect are clear. But fools don't believe and fall straight into a hell of endless darkness without even knowing it. What keeps them from believing is the heaviness of their karma. They're like blind people who don't believe there's such a thing as light. Even if you explain it to them, they still don't believe, because they're blind. How can they possibly distinguish light?
Who cares for your bhakti and mukti? Who cares what your scriptures say? I will go into a thousand hells cheerfully if I can rouse my countrymen, immersed in tamas, to stand on their own feet and be men inspired with the spirit of karma-yoga. I am a follower only of he or she who serves and helps others without caring for his own bhakti and mukti!
Many times man lives and dies between his two eternities: that of race and that of Soul... A brief parting from those dear is the worst man has to fear... Though grave diggers' toil is long... They but thrust their buried men back in the human mind again.
All major religious traditions carry basically the same message, that is love, compassion and forgiveness the important thing is they should be part of our daily lives.