Blaming the finance industry for it's services is like blaming the shipping industry. The shipping industry doesn't produce anything, it merely generates value off your goods. If it didn't exist however, you'd have to haul goods yourself, at lower efficiency, and without immediate availability. It's not absurd to expect this industry to profit for that. Of course, if there is not enough competition, or if there is collusion between shipping companies, you're going to pay an "unfair" price (for most definition of fairness).
The financial market has enough competition that most modes of unfairness are almost fully compensated for, and whether it is fair will really depend on your definition of fairness; but it's safe to say it's almost fair for most definitions, I believe. If you're trading a major stock like Apple you can be sure you'll trade for a value near the market's best estimate of what the true long-term value of that stock.
Now think of a farmer selling grains. He, an ordinary farmer, has access to the global consensus of the value of it's product at any time: he can be sure he won't be ripped off and can sell for no more or no less than the value of his goods; he can choose to sell at any time, he'll be able to do so instantly. That's a really valuable service.