Leftist dogma is like the penthouse suite of a high-rise building. The suite sits atop a majestic building, overlooking a grand vista. It holds a coveted spot, admired by some, envied by others, distrusted by many. From this grand location, it begins to look around, then decides that it's better than anything it can see below. It looks down on the rest of the world and decides that it has a better view than everyone else. Consequently, it decides to engineer the rest of the world to remake it in its own image.
Unfortunately, from its vantage point, it condemns anything that doesn't fit its view of the world. It cannot see the building's foundations, so it condemns the very base on which it stands. It starts to think to itself: "I don't really need that foundation. I'm way up here and it's way down there. It doesn't really suit my needs at the moment."
After a time, the penthouse thinks to itself that it not only doesn't need the foundation on which it sits, it thinks that the foundation is faulty. "If I could only get away from the foundation," it thinks to itself, "I would remake the world in the glorious vision I have of it."
One day, the penthouse decides to cut itself off from its foundation. It breaks free, then falls to the ground and crumbles into a million pieces.
Modern leftism owes its very foundation to the principles of the establishment of the US - political as well as moral. It is hubris of the highest sort to deny those principles in order to remake the world in its own image.