Nothing in American history can ever compare to the three centuries of Black enslavement. And, yes, white women and white activists need to be more circumspect with terminolgy, and need to acknowledge the price Black women paid for feminism. I also think reparations should happen and that Black women, IME, deserve a greater proportion of those reparations.
However, slavery still exists in the world and in varied forms. There are sex-workers who work the streets under the control of others – that too is enslavement.
I'm not convinced Atwood was drawing a comparison to Black slavery. Her book is about a modern day dystopia in which women are enslaved; I feel she was comparing the path SCOTUS seems to be mapping out for women IRL to the fictionalized enslavement in her book.