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.
You just missed the part that even those who are paid for their winnings during the course of the long run will lose in gambling so gambling is indeed design to make people lose money in the long run no matter what. Now I am not that much of a religious person but I have read all holy books and the major ones say explicitly and I am summarizing them here "in gambling you can find a bit of benefit but most of the time you will harm yourself with gambling" and this should be enough of a warning for all of the people who take warnings. People who do not care for this and continue to gamble unfortunately for them are the ones who lose money over the long run.