Tsumugi's thoughts are her own, but she's not the only one to think that way. I personally see it as a sign of maturity that you can consider listening to the other side, as long as the other side wasn't directly abusive. Safety first always. Listening and trying to understand doesn't take away all the past trauma, but it gives you a fuller image of the other person as a human being.
Having the conversation doesn't mean you'll suddenly be back to a warm and caring family. But it can put things into perspective in a way that helps you lay all the hurt to rest. It can make a big difference ro know for sure what happened because they were misinformed and/or stupid, and what may have happened because they actually didn't care enough in their heart or even wanted to see you hurt.
For me, personally, it has made a big difference when I finally started to understand that almost all of my own parents' shittiness is caused by their own repressed childhood traumas. It changed the story from me never having been loved to them just never having been capable of loving me right. This doesn't make me want to forgive them for the past, child me never will. But it kind of changes the significance of things for me as an adult.