Not all gambling addicts saw gambling as a source of income. Some started out as a fun thing too like most of us. It started as something they enjoyed and did in their spare time, especially those with deep pockets. They didn't see it as a source of income or as a way to hit it big.
I believe it's a process. They start cautiously, then start going in deeper and deeper, till they get to a stage where they can't pull themselves out anymore. I guess it's the same way with every other addiction, I may be wrong but till proven otherwise, that's how I see it.
So it's not only people that see gamble as a source of income that should be careful, but even those of us that see it as a fun thing too should be careful lest we fall in too deep.