It would be idiotic to repay the entire national debt. That would wreck havoc in the financial system because banks need to have treasuries to operate.
Also, think about this. What if the government borrows money at a low cost, spends it on a bridge, and the bridge increases the GDP and resulting tax revenue above the borrowing cost. The net result is a surplus for the government. What's the problem with that?
You could still have a national debt even while running surpluses into the forseeable future. Large capital projects, could be financed by treasuries, that sort of thing.
Capital spending on infrastructure is debt as much as the defense budget, or Social Security, are debt. It might be "better" debt is the sense of being a positive investment in the future, but it's still debt. Either you have a net surplus or you don't.
