But don't we need to worry about government debt?

That question shouldn't be dismissed offhandedly.
In a monetary system with a central bank that acts as a lender of last resort bank lending is not limited by government created base money. So does issuing bonds to fund a government deficit lead to a change in effective demand relative to running unfunded deficits? I don't see how. So what is the point of selling bonds? And if there is none, why should past deficits play a role in determining the size of current deficits?