Those “white people” claimed ownership of other human beings. Stealing their slaves liberty, property, and labor from birth.
Killing a person who claims you as their slave is justifiable homicide. Killing the children is problematic, but the adult women were equally guilty. They are legitimate targets for a revolting slave.
Tactically and strategically, Turner and his followers made a mistake when they killed the women, as it motivated the enemy. But there is no moral issue with killing an adult who has enslaved you.