Gambling isn't just for fun. Money is involved there, i do not think that "gambling should be just for fun" is applicable to everyone, especially to those people who got some of their money for living while playing on casinos.
Surely, there are those who gamble for fun as well as those who gamble for profit, so don't look at the situation from a single perspective here. People also spend a lot of money on other forms of entertainment; for instance, many spend thousands on in-game items that offer no real value. Hence, I wouldn't dismiss the fun part just because the money is involved.
We all like to get something out of the deal and not feel a hole in our pocket every time we turn around. One thing I've always considered is that I may never find a good enough source of income that works for me in a fashion that I can feel good about doing it. You never know what will come along or when it will come along.
As with most things in life, the key thing is to balance the two.
Gambling is actually only fun and exciting when it comes to real money. Only then do you feel the adrenaline and tension in your body. With the end that you hopefully win. You can also play with lower amounts, which you can easily lose, but I personally think that the tension is not there at all and then you can not really enjoy a certain amount of fun. It is difficult to say from what amount you can really enjoy it. There are people who play games without money, but that is not gambling of course.