I guess we'll have to agree to disagree.
But at the risk of keeping things going, I just want to point out that something of value is moved within the economy when the used car salesman sells somebody a car. Someone who didn't have a car before now has a car. Same with financing - banks lending money to businesses/entrepreneurs/homeowners/etc allows them to expand their business or buy a house, thereby enriching the local economy.
And yes, as you point out, people gamble as a form of entertainment. And no doubt there are some traders on the stock market who trade for entertainment as well. But if I follow your point correctly, I'd say that claiming that HFT is a form of entertainment is a bit of a stretch.
It comes down to this: what value is created by a trader holding a stock for a few seconds and then selling it?