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.