This is my area of expertise, so I'll contribute. We won't truly "default." If the risk of "default" were actually this imminent, demand for Treasuries would have dried up a long time ago. Instead, we will print currency to pay debts rather than drawing it from reserves. This action is overtly inflationary, however, and America may very well lose its status as the center of global finance (as well as the remainder of our credibility). The dollar's value will decline in addition to the actual magnitude of money supply expansion, because people will anticipate the decline and scurry out of dollar-based instruments like lemmings.
In summary: the result is severe inflation, not armageddon. And this inflation has a silver lining. For one, it makes all debts easier to pay. Second, it gives domestic producers an edge which could help us balance out our trade deficit. Not that I would advise "defaulting" to achieve either of these.
As much as I think the Republicans are reactionary pussies who spent tax dollars like soldiers on shore leave and only "found Jesus" after a Democrat was elected, I also think they're right. We need to fix this problem without increasing taxes. Andrew Mellon discovered a long time ago that increasing taxes doesn't always increase tax revenue, and we've been scaring profitable enterprise out of this country with our taxes for decades. It's time to stow that shit.