Ignorance is such a common excuse.
We didn’t know carbon dioxide could affect our climate. We didn’t know pipelines would leak. We didn’t know slaves were people. We didn’t know women could have the same aspirations as men. We didn’t know colonialism was exploitive. We didn’t know those people would be unhappy if we stole their children.
We knew all along. We just didn’t want to do anything about it.
Don’t believe those “if we had only known” people. There were other people who were telling them the truth, and they just chose to ignore them, usually because the lies were more profitable.