Ultimately, it does come down to inflationary concerns since the fed govt can, theoretically, just print up as much money as it wants. But very high inflation will destroy an economy. No one will want your money, no one will lend etc.
To avoid hyper inflation you must find a way to fund deficit spending other than just printing up more money. There are two choices: borrow or raise taxes/revenue.
Raising taxes takes money, and demand, out of the private sector. We now need more demand in the private sector, not less. More demand means GDP growth and more jobs, both of which produce more revenue for the govt from increased tax revenue and also result in less spending on things such as Medicaid and welfare/unemployment type programs. I.e., raising taxes is counter-productive.
The ability to borrow is affected by deficits and debt. This has been demonstrated in several European countries. Debt levels considered too high by lenders will result in paying higher interest rates on debt issued. This is undesirable for obvious reasons, additionally to the extent the debt is owned by foreigners it is an outbound drain of our wealth to other countries. In the extreme, debt levels that are too high mean no more borrowing (See Greece). No more borrowing, in the absence of just printing up more money and causing inflation, means drastic cuts to govt spending. Drastic cuts to govt spending means less demand and all that entails (shrinking GDP, decreased tax revenue, more spending for welfare and unemployment etc.)
Once your deficits get too high or remain too long you will end up with debt that is too high. Once the latter happens 'painful medicine' is inevitable. It becomes a matter of 'when' not 'if'.
Fern