The constitution didn’t get us $20T in debt. You can’t just wave a copy of the constitution and get us out of 100 years of deviating from it.
It may not be constitutional for the government to own that land, but it is reality. So is the debt.
Most of the land in the United States originated as federal estate. One of the huge statesmanlike acts in the earliest days of the new Republic was the renunciation of western land claims by the original 13 states. Had they not done that, Virginia, Pennsylvania, New York, and others would still be fighting wars over who owned a particular mountaintop or swamp in what is now West Virginia or Mississippi. At a stroke, all the land between the crest of the Appalachians and the Mississippi became a federal domain.
Then came the Louisiana Purchase, the purchase of Florida from Spain, the acquisition of the Southwest and California from Mexico after the Mexican War, the Gadsden Purchase, and the purchase of Alaska. All of this was acquired by the federal government and was originally federal estate.
The exceptions west of the Appalachians were Texas and Hawaii, both of which were independent republics before entering the Union.
Until the late 19th century, the federal government was committed to divestiture. In fact, land sales and tariffs were the major sources of federal revenue in the early days. As the frontier moved into the desert and mountain west, however, the land because unsuitable for yeoman agriculture. The principal value was ranching, timber, and mining. Congress balked at transferring huge tracts to private corporate interests at fire sale rates. The decision was made to retain federal ownership but to lease much of the acreage via the BLM and the Forest Service. We are left with the huge blocks of federally owned land in the west, and a rogue environmental movement that is working overtime to shift management objectives away from multiple use and economic exploitation to park and wilderness type management, which is hamstringing traditional western industries. That's what the fuss is about.
I agree that the feds own too much land in the west and that big chunks of BLM land, and perhaps some Forest Service land as well (NOT national parks, wilderness areas, national monuments, etc.), should be transferred to the states or privatized. (I would use the proceeds to enhance park holdings in the east, where the feds own very little land and where high population densities create a need for expanded park resources.) The politics of this are intricate. But we need to recognize that the feds have always owned most of this land. The amount of private land that the feds have acquired over the past 50 years is relatively small compared to the vast tracts that the feds have always controlled.