They don't need to balance their budget, but they should not let the deficit explode near the end of an expansion as they are doing.
As a rule of thumb, if you keep the deficit/GDP ratio under 3%, then the Debt/GDP ratio tends to decline. The near-term problem is that before the next recession hits we will have a deficit near $1 trillion, the Deficit/GDP ratio will be > 3%, so the Debt/GDP ratio will also be rising. All make it difficult for politicians to come up with an adequate response...