The US, of course, does not need to have its government debt funded in particular. However, we cannot have the rate of GDP growth required to help investment banks gin up the next bubble economy unless we get capital inflows to allow us to have otherwise unsustainable current account deficits.

Providing official debt as an instrument for neo-mercantalists to use when discounting their exchange rates against the US$ is one (among many) elements in encouraging those capital inflows.

I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.