"If I'd 'a known, I'd've picked my own cotton!"

Well, I'm not attuned to how racism works in the States, but I'd have thought that was an anti-racist slogan, if anything - essentially saying "I didn't appreciate how Black people were being oppressed and exploited all this time".
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I don't know how I feel about the flag issue either because people were enslaved as the Constitution was being written by the same people who were slaveowners. Should I also fear the U.S. Flag?

I was interested to see Rubylox say that - it's something that had occurred to me too. The same applies to the Union Jack here - in one version or another it was the flag that at one time flew on ships protecting the slave trade, and at a later time on ships that trying to put it down.