I think the idea that your people/ancestors/country is uniquely horrible is itself a kind of bizarre and twisted sublimated notion of superiority.
Human history all over the world is rife with genocides, slavery, torture, forced expulsions, institutionalized discrimination and hateful treatment of minorities, and notions of ethnic supremacy. America isn't the slightest bit special in that regard. Every nation on Earth is built on the blood of somebody, and most of them aren't wallowing in guilt over it, nor should they. It's the normal human condition.
I also don't think it's productive. People are not amenable to the idea that they should share guilt for crimes that happened before they were born - the moral sentiment that crimes pass down through blood is mostly extinct, so that line of argument tends to alienate people. Further, it places the past in an anachronistic lens of modern morality - in today's moral universe, every single person of the past was wicked. So what's the point of harping on it? None of us would be here without them, nor would today's moral universe even exist, so people are necessarily going to feel some gratitude for those that came before, so again, you're alienating people who might otherwise be sympathetic.
If you want change, just make the argument for that change and look forward, not back.