How can one be proud of a country founded on black slavery and Native American genocide and poor exploitation?

To a degree, I agree. But there is not one civilisation in history, who hasn't had slavery, genocide and exploitation. But I take your point. The point is the balance between the crimes and the virtues of the past, to condemn heavily what was wrong (like slavery) and it's modern effects (like racism, like unequal racial wealth distribution) and fix it in the present. But, as a European, I sometimes find it sad that successes of European civilisation (including American and Canadian etc.) are ignored, and focus on the bad points of are history are exacerbated. European science has probably saved many more than killed by a European gun, European culture has made it moral that such questions should always be asked. It doesn't make it right, I agree, but it's something that should be remembered.