> Buying a stock on the secondary stock market is not investing in the economy.

Of course it is. Buying a piece of a company is investing in it.

> Buy that logic, high-frequency traders are investing in the economy.

And they are - even if they hold a particular stock for a millisecond. The aggregate invested across the market is what matters.

It's a bit like calculus. All those infinitesimal bits add up to real amounts.

> That doesn't follow from what I said.

Maybe you can explain why banks offer free checking.