Regardless of who benefits between the two then I can only say that they are just part of the industry that serves your needs. Nothing is free and both use their customers to make a profit - it's worth it for what and who they serve, right?

You need the casino to serve you to gamble - so you have to pay them instead of just betting your money. The same thing about brokers - you have to pay trading fees ^{[or whatever]} if you use the facilities they provide and it is all a win to win situation between customers and industry players. There is no blackmail because you have all agreed to the terms of service - if you say it's blackmail then re-read the conditions for using their services.