I think this is the overlooked key point in these discussions of MDMA or other treatments as remedies for PTSD: it brings on the ability to see yourself and your actions with compassion and forgiveness that is not present in baseline consciousness.
For my own healing of trauma (which did not involve the use of MDMA), that has been the key. And letting go of deep resentment towards others (e.g., parents, former partners, lost friends) happened pretty much immediately, once I was able to have self-compassion and forgive myself.
As promising as the research around MDMA might be, it's still likely to be a long time before it has clinical and legal approval in most jurisdictions and even then it may not be the be-all-and-end-all for emotional healing.
Whereas there are techniques for bringing on self-forgiveness that are already available, though not yet accepted in the mainstream.
Hopefully that may start to change soon.