I don't disagree with what you are saying.
I don't care much if people make a fair exchange if no one is hurt.
My point was to answer the question "Why is gambling immoral" and gave reasons why it could be looked at that way.
Morality is a gray area that society comes to a concensus on but is also determined individually.
When I take this to purchasing child porn that changes things.
Purchasing child porn doesn't hurt anyone.
Watching it doesn't hurt anyone.
But if there was not a market for it than that eliminates the distribution of it and will eliminate the hurtful act of producing that for money.
Most would agree that purchasing child porn is immoral yet it works with your statement of voluntary expenditure.
So voluntary gambling isn't necessarily moral.