While this is partially true:

1. Sovereign nations absolutely can and do default. See, Russia in the 1990s and the LTCM fiasco.

2. Even though they do not have to default and can always print money to pay their debts, doing so causes inflation. How much inflation it causes is proportional to how much money is printed.

Now, the dynamics of inflation are pretty complicated, so in certain circumstances you can get away with it for a while. But it is not the case that the government can print money indefinitely with zero consequences.

Unlike at the micro level, at the macro level your spending is my income.

That alone changes (almost every) received microeconomic intuition.

The fed could find itself in the position of fighting a structural imbalance such that for every dollar lent to the government the deficit increases by 1.X dollars. This would be the case under rampant corruption, rampant inflation, or an economy collapsing.

That has negative consequences that are papered over by making simplistic statements like that. The debt is still bad and going to result in bad things happening, and no platitudes from the Fed are going to change that.

In reality, savings and debt are basically two sides of the same coin - one is a promise for future consumption, and the other is a promise to forgo future consumption that balances it out.

One of my favorite simple models is sectoral balances - you can divide US dollar holders into domestic and foreign categories, and then divide up the domestic category into the private sector and the government (leaving 3 categories total).

If you don't print money, the net saving should all add up to zero. If the government is running a surplus, that means the combination of the private and foreign sector is going into debt. If there's a trade deficit, then the combo of the private sector and government are going into debt. Etc.

People can still be against government deficits with such a model, but it's not because everyone should save up at the same time (they literally can't). It's because they want the private sector to go into more debt, and are worried about government debt "crowding out" private sector debt. And more private sector debt isn't always a bad thing - in practice it might mean more housing, factories, and other sorts of investments that debt finances.