Again, it is on emphasis. I think slavery was a horrible sin. I don't think it defines us. You may not think that either, but there is a very large contingent of people to the left of you who very much do. They have a whole project based on a date where that is the very premise and if they think we are great and have been great, they have a weird way of showing it.One might argue that you have that exactly backwards, that the conservatives would downplay just how bad the bad was. One might remember Lincoln's words on the morality of the Civil War: "Yet, if God wills that it continue until all the wealth piled by the bondsman's two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood drawn with the lash shall be paid by another drawn with the sword, as was said three thousand years ago, so still it must be said "the judgments of the Lord are true and righteous altogether." One might recognize that our national sin was not some sideshow to our national greatness, but actually a huge, cosmic-level sin that affected millions of lives.
America is great. America has been great. American can become even greater. I don't need to downplay the horrible things America has allowed to believe those three things.
We are great. We have been great. We will be greater when we start moving forward instead of continuing to dwell on what was like it is the here and now.
And we will go round and round and I am not convinced your opinion above is expressly wrong just as much as I am convinced mine is right.