Hinduism and Buddhism supports the rebirth. Let us assume, rebirth is true. We generally don't realize what happened in previous births. Then what is the use of cause and effect of karma or rebirth ?
If I am not even going to know what I have done and what I am now, then either rebirth is not true or the thing that rebirths is really not what I am now thinking as "I". so without realizing "What Iam?", does rebirth really matters ?