"the lessons we’ve learned from the centuries when our biblical texts were used to justify slavery, discrimination, segregation and oppression of people of color and women,”
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In regards to slavery, the bible never justified it.  In the context of a world in which slavery was everywhere, it tried to make it a little better, to impose some rules.  It was also the foundation for getting rid of slavery.
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As for oppression of women, the same thing.  In the world of Paul and Jesus, where physical realities imposed roles on which survival depended, the bible exhorts husbands and wives to subject themselves to each other. 
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As for same-sex marriage,  it is a biblical oxymoron.  This is not to say that the federal government should not support the idea of a gender-free partner contract.  But to assume that this is somehow the same as that of a man and a wife, the biological basis for the procreation of the human race, and the idea of a marriage known to Jesus, is delusional.