Comparing the Federal Government to either household (as I've seen in the past) or to business spending as the last couple of posts here have, is comparing apples to apple trees.
The government can raise revenues at will(taxes), or create more money at will(create more debt). Business and households do not have this feature, they are forced to live within constraints of cash-flow and/or the free economy's willingness to lend to them.
Still, there are limits to how much a government can extract based on GDP (or as the US does, extract from others GDP through reserve currency status or force). Also there's always the possibility of revolution if the economic conditions become too poor.
I'm not say'en fiat currency will all work out in the end. It may or may not, depending on governments ability to constrain itself and look both short AND long term. However, it's not going to run short on cash flow or it's ability to create debt at any time in the near term.
I do, however, agree that the most recent deficit binge is a complete waste. We should be building an infrastructure to keep the US competitive for the rest of the century, not corporate tax cuts for stock buy-backs.