The numbers on that are at least somewhat questionable. Even ignoring that you'd crash the market (thus it's not actually worth what it first appears to be) what is the total fuel cost to adjust the orbit of the target asteroid to land the entire thing back on the earth? Because that's what you're doing bit by bit as you shuttle loads of ore back.

Now if you have space based manufacturing or fuel production on the other hand ...

That's the point. Basic rule of thumb: anytime someone is arguing that the military will fund something, they're wrong.

Its not a real argument it's just used because to most people the military is a big mysterious thing they don't understand which they think has an infinite budget for things.