That's not actually true, particularly, there is no necessary reason why, as long as economic growth can be maintained over the long term (even if that's not always the case over shorter terms) a country can't sustainably have an ever-increasing debt balance, without ever paying any of it off other than by issuing new debt.
Even if it was true, if government deficit spending increases stimulate economic expansion, the tax funds to pay for the spending can be produced by the spending.
"if government deficit spending increases stimulate economic expansion"
Which it didn't and hasn't - the best times in our economy were when the government spent and taxed less (e.g. 1946 & 1948 fiscal changes).
"the tax funds to pay for the spending can be produced by the spending"
No, they cannot and that's just twisted logic - you cannot spend your way out of debt
If that was true, corporate finance would be a lot different.
But not out of funds that they would have had without the expenditure. So they have literally given up nothing.
Its not "free money", its taxes paid by taxpayers. There is no "free money" in government.