The debt is manageable right now - though way higher than it should be and getting dangerously huge - with total unfunded liabilities figured in it's probably upwards of 75 trillion or higher
It's like a mortgage - if you make 60 k a year and keep spending reigned in you can afford say a 150 k home because you pay on it over time, the problem is that when the interest equals the principal borrowed you can't pay it off - we are heading there
As the debt gets bigger we have to take more money from other areas to cover the interest payments - so less $ for education, infrastructure etc... and eventually with all the leeches living off the system it will implode
Capitalism can be a great thing, but must be handled with care or it can be a train wreck