We need to address a few errors in your story.

First,

This is why free trade creates prosperity: it encourages virtuous pay-it-forward behavior.

Pay-it-forward, expects no pay back. The quid pro quo is you will favor someone else, a third party.

Second,

The answer is the government spent that money into existence.

No, the first money was barter turn to currency. First salt, then gold, silver or gems turned in to currency.

Third,

The government didn’t tax anyone to raise the money to pay the workers to build the road.

Is bullshit. The government was collecting taxes and paying in gold and silver long before anyone would work for fiat.

Fourth,

In fact, it need not tax at all. Since the government can simply print money as bills come due, taxing is in a sense optional.

No it can't that is against the law and maybe for good reasons.

I can't read a paragraph of your story without finding errors and I agree with a proper MMT.

TEK