For those who hold that there is only an “All-Soul” and no reality to the individual soul, there is clearly no rationale for there being any necessity for rebirth, as the growth, and reaping of consequences at the individual level basically would have no meaning. There would be an “All-Soul” undertaking actions through innumerable forms and beings, and it would not really matter that the consequences would fall on others, or on future generations, rather than the individual carrying out the action.
We actually can see that the action of the individual can and does impact not just the individual undertaking the action, but others, both in the present and in the future. Some religious or philosophical directions have created colorful descriptions around this phenomenon when they speak of the “sins of the father being visited on the sons” down through many generations.
The impact on the individual becomes real, and requires rebirth for its effectuation, if we attribute a reality to the individual soul. The impact on others nevertheless still occurs and becomes what we may describe as something of a “collective Karma”. Sri Aurobindo discusses this with the following: “What I sow in this hour, is reaped by my posterity for several generations and we can then call it the karma of the family. What the men of today as community or people resolve upon and execute, comes back with a blessing or a sword upon the future of their race when they themselves have passed away and are no longer there to rejoice or to suffer; and that we can speak of as the karma of the nation. Mankind as a whole too has a karma; what it wrought in its past, will shape its future destiny; individuals seem only to be temporary units of human thought, will, nature who act according to the compulsion of the soul in humanity and disappear; but the karma of the race which thy have helped to form continues through the centuries, the millenniums, the cycles.”
Of course, this form of collective karma is not the entire picture, and the life and karma of the individual is inter-woven with the life of the society, with impacts moving in both directions and reflecting the evolutionary development through the operation of Time.