After a carefully thinking about the topic and the reality of gambling, I want to agree with you partly because that statement is true but with some exception. A lot of people do lose in gambling but not everyone is losing so we can say that gambling is designed to give the house edge so they remain in profits. Part of the money lost by majority of the people will be used to pay those that would win and the difference being the profit the casinos will make. This is how I think gambling is designed.
I disagree with the discussion. Casinos, being fully-fledged commercial businesses, have no interest in deliberately losing their customers. If you have 100 customers and all 100 lose, you'll almost certainly lose a significant portion of them.
We're talking about legal casinos that protect their customers (and therefore are fully regulated).
To simply recoup their profits, they can give a percentage of their profits in winnings; otherwise, they wouldn't be able to sustain themselves and would therefore be doomed to bankruptcy.
It would be counterproductive to lose your customers just to steal their money.