The housing market collapsed because people lost faith in the loans. China and Japan might decide one day that US debt is worthless, and in doing so would wreck not just our economy, but theirs, and probably the world economy as a whole.
So it is a dangerous game, and at some point we do have to pay it down, but comparing it to the housing market is like comparing the US to a nation like Ecuador, or some other nation that needs debt relief.
Also, as a percentage of GDP, we are only now approaching WW2 levels. The debt decreased as a proportion of GDP during every presidency until Reagen, and has been rising ever since. The original 'Keynesians' did pay it down after it got us out of the great depression, all the way down to 30%. Take that for what you will.