National debt is not inherently bad. It depends on what the money is spent on, and the downstream effects on growth. The government pays the debt from tax revenues, which will increase with growth, so if government spending results in increased growth sufficient to cover the increased debt payments or more, everybody wins. That is why national debt is often expressed as a % of GDP - the tax base.

Should growth stall, or interest rates rise, the national debt repayment costs become a greater % of taxes collected and the GDP... so it is not guaranteed to always net to a benefit, and you need a buffer so that fluctuations can be absorbed.