Government debt is a burden on future tax payers. Government debt is financed largely by the sale of Treasury bonds. Those bonds need to be repaid at a set date in the future with interest. How are they repaid? Either by the sale of more bonds (kicking the can down the road, something all governments love to do), or out of government revenue, i.e. out of taxpayers' pockets. So either spending is reduced in future every time we go into debt, or taxes are increased. The only alternative is the sale of assets.
More importantly, government spending does not stimulate the economy. If the spending is from tax revenue, then the economy has already been reduced by at least the amount of the spending. All that is achieved under the best case scenario is a shuffling of deck chairs. In reality, the economy actually shrinks due to government spending, since money is siphoned away from the more productive sectors of the economy and redistributed to the less productive. This is even assuming 100% throughput and no waste, which is a hopelessly unrealistic assumption.
If the government spending is deficit spending (debt), then the economy in the future is being reduced by the amount borrowed + interest, for the best case scenario of increasing the economy now by the amount borrowed. Of course the spending is still subject to the same factors of being redirected to less productive sectors of the economy and churn (waste).
Governments (and people who support them) like to talk about creating jobs and stimulating growth, but what they never, ever mention (because it's easy and convenient to ignore and impossible to measure) is the number of jobs either directly destroyed by their intervention or that would have been created had they not intervened, and likewise the economic activity that was directly destroyed by their intervention or would have occurred had they not intervened. These things cannot be measured, as we can't take a trip into an alternative reality to observe them, but they are very real. This is known as Opportunity Cost, and is one the foundational concepts of economics. Any economic analysis that leaves opportunity cost out is at best completely wrong, at worst deliberately deceptive. And most of what passes for economic analysis in a political context does leave it out. Including pretty much all of the whinging about the budget I've observed thus far.
