If you think of an economy as a body, money is like the blood of the economy. Right now, too much of the money is in the hands of too few people.
When too much of the blood is all pooled up in one small part of the body, the rest of the body suffers.
These people just want to sit on their money and let everyone else do all the real work. The debt itself isn't the real problem. It's the people who own that debt.
Also, the $20 trillion figure is going to get even worse. As long as politicians/lawmakers keep on using tax dollars to buy votes through government spending, things are going to keep getting worse.
Thats why more people should buy bonds and save and invest.
What if we just don’t pay it back?
That would cause another recession.