Since the GDP contains all government spendings and debt, it is obvious that debt and spendings only increase "economic growth". But if you call a spade a spade and realize that 100% of government spendings is taken from products of the market, then the real GDP (RP) will be defined like this: RP = "Official GDP" - 2 * (gov debt and expenditures).
That would only be true if 100% of government spending came from taxes and the government didn't spend anything, it does not. Deficit spending comes from people investing in the government, and a non-trivial amount comes from foreigners. You buy something from Walmart -> China gets USD -> China buys US treasuries. You got a product, the US government got money, and the Chinese got left with an IOU.
Moreover, government spending doesn't vanish into a blackhole. If I tax a dollar from you, and then build a highway or launch a GPS satellite or educate a child, I not only put your money back into the economy, I also left lasting changes that improve efficiency.
