I couldn't agree more with those gamblers saying that they gamble just for fun because the truth is that people gamble in the hope of multiplying their money. But from what we have witnessed and seeing the sentiment of the majority, we definitely see that they feel disappointed when losing. Which is not really the behavior of gamblers who just think about entertaining themselves. A real gambler never seeks winning but pleasure and fun.
Even if it's gambling for entertainment, I don't think it's correct to say that you shouldn't feel any emotions. People entertain themselves by watching movies/sports, playing video games, they also feel emotions and those emotions are part and parcel of having fun.