Capitalism is based on there being a customer. All the capital in the world doesn't do any good if there's not a buyer on the other end. Another argument for a strong middle class.
Of course, if there is no customer, there can be no sale. However, the sale itself isn't always the point. Sometimes people do things just for the fun of it -- and that's capitalism, too.
Yes, they need a healthy middle class if they want to keep a capitalist economy going. Here's the depraved little secret: they don't actually care that much about having a capitalist economy.
Social elites are almost always parasitic and actually quite non-ideological. If we were a communist or fascist state, it'd be the same people in charge, but instead of being corporate executives, they'd be government bureaucrats. They don't give a shit about "capitalism" or "socialism" so long as it's them on top. The ideology is something they tune to the peasants' shifting tastes.
It's not about economic well-being for them. It's about status. In a robust capitalist and technological economy, they get private jets. If the U.S. becomes Third World, they get white maids. Both are essentially status symbols, and they don't have an intrinsic attachment to one over the other, but they'd rather reign in hell than serve in heaven.
humans have needs.
there is no shortage of customers.
before currencies, there is trade. who is the customer in a trade before currency? it's an exchange, not a purchase by a customer from a seller.
I fail to see how these sentences form an "argument".