The topic of slavery is a non-sequitur to the OP.
But I don't think it is. If you are going to try to justify your ideas about gender by appealing to what is traditional and Biblical, then I think we get to point out other things that are traditional and Biblical and ask if they are justified by the same means.
When you write about sexism:
How about the system which has served most cultures of humanity for nearly all of of human history.
and you write about slavery:
nearly all cultures practiced slavery
... then I think the question of slavery is fair game.
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