If you believe that governments can and should intervene in the economy, then its not an either or question regarding deficits and surplus. The standard Keynesian model (relevant to Ed Balls) is that you run budget surpluses during periods of positive growth so that you re able to run deficits in period of recession. This, in theory, smoothes the natural cycle of economies.
In the UK we rarely run budget surpluses BUT labour did at one point. Then in the "end of boom-and-bust" hubris of Brown and Balls they screwed up badly by running an increasing deficit at exactly the wrong time, thereby reducing the policy options in the crisis. As a Keynesian economist Balls has admitted as such (see previous speeches to Fabian Society), but not as a politician (see this week). The Tories were as bad in the previous recession to be fair, but there are fewer Keynesians in their camp who would know better!
Before you reduce the stock of debt you have to stablise it and there is simple formula
Public fiscal surplus (PFS) = taxes - expenditure ex interest on debt
The PFS that stabilises debt = the public debt ratio (debt/gdp) x (LT interest rate - nominal LR growth)
So the higher the level of debt, the greater the gap that is required between IRs and growth. In the crisis, people started to believe that in some countries the PFS was impossible to achieve since the maths means that governments would need to raise taxes a lot or reduce expenditure a lot and that both/either/or wold have damaged the economies too much.
Of course, if growth > the interest rate on debt, things take care of themselves. At the moment that is not the case, so we need to run budget surpluses of 1-1.5% of GDP just to stabilise our debt. Try doing that in the middle of a slowdown! At least the dynamics are improving slowly.
Also before we give any Chancellor too much grief, just play with the sensitivities in that equation.