The knowledge of the world can be divided in two main categories - first is the scientific knowledge based on observations, experiments, and deductions. These are accepted as truth till some new theory comes which can explain that in better ways and give better formulas and experimental verifications for them. The science subject is full of such theorems, theories, and deductions and the science or engineering students know about these things in details. Second category of knowledge is hypothesis based on the spiritual, religious, philosophical, and cultural experiences of our ancestors and these are available in form of some scriptures and books which are available in various societies and communities and those who believe in them follow them religiously and persistently throughout their lives and leave this world believing that doctrine only as the true one and all others in the world as wrong. In fact most of the wars and confrontations happened due to those differences and confrontations.
The theory of Karma is one such hypothesis which is believed by many communities including many Indian people. No one knows whether it is true or not and we can discuss that for hours without reaching to a logical and rational solution. Actually, this theory was propounded by some scholars when they found that some people suffer in this world while some others enjoy. So they told that at least do something good so that one's next life becomes better. So, this was a management technique or tool to motivate the people to do good. Those who believe in it must follow the good and sacred paths in life and should not indulge in dishonesty, crime, stealing, harming others, humiliating others, killing others, bribing, corruption, torturing etc and the list of these forbidden attributes is quite long.
Those who are interested to learn more about the theory of Karma and its practical offshoots can refer to the great Indian classic Bhagavad Gita where through Lord Krishna the teachings on this subject are made. There are some good translations of this scripture in English as well as regional languages and one can choose the language of ones choice for reading this great work. The translation made by Sri Prabhupada (Abhay Charanaravinda Bhaktivedanta Swami) the founder of Hare Krishna movement deserves a special mention here.
So, whether it is true or not the beauty of this doctrine is that the human beings are asked to do good in this life and reap the benefits, if not today, then in the next life. Many people from western countries are also impressed with this great ideology and follow it. So I do not think there is anything wrong in this philosophy even if it was the handiwork of some scholar in the past. People are blindly following their religion, beliefs etc and why not to follow this great piece of advice from our ancient scholars. This presumption of Karma of past life associated with the present makes our life happy and contended because even if adversaries are there we can very well attribute it to the past life and if we inculcate this theory in a big way in our children, the coming generation, the society and its inhabitants can reap the benefits in this life itself.
I have tried to explain the issue in a simple language but it is a very deep and complex subject and those readers who want to learn more should refer to the translations of Indian Vedas, Upanishads and other related scriptures.
Knowledge is power.