Rates will rise, but that doesn't affect the interest rate for bonds already issued, of course.

No disagreement on opportunity cost - I was responding to the prior posters assertion that the government "took on gargantuan debts to brush [the financial crisis] under the carpet".

I guess you could say that some of the debt incurred during the crisis was attributable to a loss in tax revenue as well as the cost of the approximately 1T in stimulus funds between the Economic Stimulus Act and the American Recovery and Reinvestment Act. That's still a relatively small portion of the total debt of ~16T which is probably mostly due to a mixture of the Bush tax cuts and growing Social Security/Medicare outlays.

Bonds already issued were bought by people like you and me and pension funds who will now be paid many years of below-market interest. It's also embedded into the inflated pricing of every other asset that will have low expected returns going forward. No matter how you seem to want to do funny accounting, you're still paying that cost.

Yields (rates) are pretty much directly correlated with inflation. Low rates, low inflation. The real return is probably the same.

Which is not true at all. US real yield has gone from less than -1.5% on the short end [1] to around 1% recently across the yield curve. Historically it was around 2%. Not only that, the term premium is still likely negative [2]. The financial repression was real.

[1] https://www.treasury.gov/resource-center/data-chart-center/i... (Note that there was a further 80 basis point spread between nominal overnight rates and the nominal 5 year rate, so real overnight rates were really really negative.)

[2] https://fred.stlouisfed.org/series/THREEFYTP10

This does not mean that without low interest rates things would be better. (And I'm not saying Greenspan et al. handled the early 2000s well. But I'm also not convinced that the economy's set point is the federal funds rate. I think it's just an aspect, and business fundamentals - like real aggregate demand, which is much more sensitive to disposable income than to interest rates - are much more important for growth.)

The government does not have opportunity cost for money that it prints out of thin air.

The Fed can do that. Congress not so much. (Sure, technically Congress can legislate money into being, but there are good reasons why it uses bond auctions to fund its accounts.)