I think that depends on your definition of 'America'. I think that it means two different things depending on whether you are left or right. The left see the founding principle as something broken needing to be fixed, and the right see it as something to be returned to.
The right bemoan the ending of America as the ending of the American Dream - the ideals, it's founding principles. The left see it as an opporunity to hand responsibility for their decisions to someone else so when they fail, they won't be responsible.
Except that it never existed other than in mythology.
For centuries, this country - like all other countries - did NOT ascribe rights of life, liberty and property to all of its citizens. When it was first being written, it applied to white males who owned property. Slavery existed for the first century of this nation's existence, and a whole race of people was disenfranchised for another century in large swaths of the country. Women did not have full legal rights until 1920.
The ideals of America are the best in the world, IMHO. However, we should not idealize a past that has never existed. That is what conservatives are guilty of.
Perspective.
Throughout much of history, society depended on the subjegation of others as slaves. The word comes from Latin and meant those from the Slavic countries because that is where the Romans took them at the time. Human rights have suffered from this paralax view since before history was written. Slaves were used by Pharoah before the Bible was written.
The slavery of the USA was not unique nor was it original. It was the end of the institution in North America and an afront to the stated ideals of the Founders when read literally, but not with the paralax view used by the intelligencia of that time or any time before then.
That Jefferson owned slaves does not reduce the power, the eloquence or the prima facia truth of the words he wrote. "We hold these truths to be self evident, that all men are created equal..." What a thought this is. It is, by and of itself, the Revolution.
The drive to attain this ideal has changed the world. Literally. If we believe that this thinking might have existed in the past and we should try to re-attain it, I don't know why you would think this is bad. If you think that we should condemn those who believed this in the context of the world in which they lived, again, I don't know why you would think this should be done.
If a lofty ideal is held up to emulate, one that has changed a world to one of Democracies from one of Monarchies and Dictatorships, what could possibly be bad about that? Please recall that there were about 5 democracies on Earth in 1890.
In light of this, you are defending group-thought that delights in picking fly poop out of pepper while the feast rots on table. Go ahead and eat the feast today. You might end up with a little fly poop, but who cares? If you can't stand the thought of it, then don't use the pepper.
Why condemn Jefferson or Franklin or Washington or Adams for seeing the world in the context of their time. Why not exhalt in the fruition of their thoughts and their ability to see the furure in the context of the potential of their dreams.