Yes, we must not spend much money and only use the money we can afford to lose. That will prevent us from the big lose while we can enjoy gambling as an entertainment.
I agree with your statement that we should see casino as a place for entertainment. However, if we compere casino with some other services to entertain people, that we will see, that other options. for example, video games, bowling, shooting contests, they all give you something in return for your money. You actually have an opportunity to spend some sufficient time having fun or purchasing something you will own in the end.
But the thing with casino is that you will have fun, no doubts, but you will be satisfied only your money multiplies. If you lose, you will probably regret playing those games or you will feel sorry for your loss. Those emotions are much more negative, then losing in a video game, for example. And when we have to deal with such strong bad feelings, it is hard to say that they are part of an entertaining process.
Of course losses are an integral part of the entertainment process. The hope of winning and winning itself bring us positive emotions, but as we all know gambling is not possible without losing because it is a zero sum game. That is why I believe that losing, although it brings negative emotions, it is also part of the entertainment process.
Besides, winning in a video game does not bring as much vivid emotions as winning in a gambling game. Because in a video game you risk only your time.