Why does QT have to change history?

Rating: 6/10 (27 July 2019)

The Basterds killed Hitler. Now, the actor and stunt double saved Sharon Tate. To me, changing history to such a degree ruins a film. Sharon Tate and her friends were brutally murdered. Tate had her baby cut from her. I was hoping not to see that once I noticed Sharon was a main character, but come on, killing the murderers before they kill? To disrespect Sharon like this in unforgivable.