I would rather phrase it as: "casinos and slots machines are intended for the house to be profitable". And in order for that to happen most gamblers need to lose their money in the long term.
I read it somewhere that the percentage of people that are making money from gambling is 3%, but I also saw that it may be up to 5%. That means 95 to 97% of people are losing money while gambling. If that is true, I think what OP said is still true also but you are just more accurate. I said OP is right because some people just want to earn money while gambling and that was the beginning of their losses which might even lead to gambling addiction. But having it in mind that you will most likely lose, you will have it it mind to use just small amount of money to gamble.
I am not an expert, though, but that range of percentage when comes to people who get profit from gambling sounds a little bit too optimistic in the favor of gamblers. It could be translated as 30 in 1000 gamblers are making money from their sessions... That does correlate with reality if you asked me, if so it would be more common to see people talking about their wins on social media and casinos would need further advertising of lucky gamblers in order to continue bringing more people. i would say the actual percentage of people making money on casino is between 1,0% and 0,0%. Perhaps, 0,5%