You can observe this by how easy it is to fall into the trap of thinking that destroying the money would be a huge waste. It wouldn't. Money, by itself, has no value. It's only useful in how you can use it to obtain goods and services. Destroying money reduces your own ability to obtain goods and services, but doesn't actually destroy wealth, as everyone else's ability to obtain goods and services increases to compensate. While wealth is typically measured in money, wealth consists of goods and services.
The fact that the money recirculates in the economy is irrelevant to the question of waste. If they wasted the money, it essentially means that the goods and services purchased with it were squandered.
So, forget the money for a moment. Analyze it like this: a bunch of engineers and technicians spent thousands or millions of collective hours. High quality aluminum, steel, electronics, etc., were used. And the result is a spacecraft. That time and those resources could be used to do something else. Perhaps something better, like build schools or factories.
That is the argument being made. I'm not saying it's necessarily correct (this mission doesn't seem like it's very expensive in the grand scheme of things, and the benefits for science, technology, and just plain prestige seem well worth it) but it is at least sensible in its foundations.