I mean, it'd be hard to build something like a steel mill or an oil refinery without financing.

That's what stocks was invented for. Initially.

You want to build steel mill, you invite others to participate in that adventure and then you share future profits and losses of your common enterprise. Fair play and perfect source for initial financing of big projects. Very capitalistic.

No usury was ever needed for capitalism.

But then some bastards proposed stocks to be freely tradeable in stock exchange gambling. And that totally ruined the whole idea.