Imagine if America's biggest mistake was that blacks couldn't run for public office until 1978 because the founding fathers were superstitious or perhaps they thought that it could cause further division in the country. Certainly they had strange thoughts on intermarriage and mingling. But no slavery, no segregation, no 3/5ths compromise.
That's basically what the church is guilty of. It was probably far more liberal than the prevailing institutions of the time. The church was even a refuge against the US govt from many fleeing persecution. The one practice remained until it seemed worse than the US government.
Yet, the church is still perceived as a highly racist institution today. It's unfortunate.