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?
The universe that we inhabit and our shared perception of it are the results of a common karma. Likewise, the places that we will experience in future rebirths will be the outcome of the karma that we share with the other beings living there. The actions of each of us, human or nonhuman, have contributed to the world in which we live. We all have a common responsibility for our world and are connected with everything in it.
O youth or young man, who fancy that you are neglected by the gods, know that if you become worse, you shall go to worse souls, or if better to the better... In every succession of life and death, you will do and suffer what like may fitly suffer at the hands of like. This is the justice of heaven.
Delusions are states of mind which, when they arise within our mental continuum, leave us disturbed, confused and unhappy. Therefore, those states of mind which delude or afflict us are called 'delusions.'
Surely if living creatures saw the results of all their evil deeds, they would turn away from them in disgust. But selfhood blinds them, and they cling to their obnoxious desires. They crave pleasure for themselves and they cause pain to others; when death destroys their individuality, they find no peace; their thirst for existence abides and their selfhood reappears in new births. Thus they continue to move in the coil and can find no escape from the hell of their own making.