Since one of the largest motif's in Beloved is memory, I decided to look up what a memory actually is and how it works. I found out that there is no one place that our brains will store memory. Instead, the brain tends to divide a "memory" up into separate parts of its system and then put it back together later. For example, if you remember riding a bike then your knowledge of ho to ride a bike may be stored in one part, safety rules (or purposeful disobedience of them) may be in a different part, and the nervous feeling you get when a car veers too close may be stored elsewhere. Each element of a memory is encoded in the original part that created the fragment (visual cortex, language area, etc.). If you want to recall a memory, you need to reactivate the neural patterns created during the original encoding.
However, this kind of broken up storage leads to small alterations in memory and, with time, large changes. In Beloved there is particular emphasis on the infanticide memory, as we see it from the perspective of many different characters. Perhaps the reason Morrison added this was to ensure we did not find that the memory has been subconsciously changed to look far worse than it may have been in reality. After all, how much would you remembered after such a LONG period of time? If you're argument is "its something you would never forget, because of its atrociousness", then I can counter it. Those people who witnessed the events on September 11th, 2001 were very surprised to, years later, learn footage of the event was played on television the day AFTER it happened, not the day of the attack. The reason for this is that they had been going over the memory constantly in their heads so many times that they changed it. Many other witnesses also attested that, after being shown footage of the attack, said that "it didn't happened that way, it happened this way" and proceeded to tell what they remembered, and no too stories were similar.
Memory changes over time, and with it the emotion experienced during the actual events. It may be possible that Morrison wanted to assure the reader that the action they read about was exactly what happened by giving them multiple perspectives. I have seen other writers do the same thing to emphasize "realness". This may also be the reason why the infanticide we see in the book appears in a FLASHBACK and not a memory, further recognizing it as the truth.