I don't believe in morals or eithics. But playing poker makes me feel bad because of all the harm I am probably causing some people, so I'm kind of in the same position as you.

For those who have eithics/morals, I don't see how it can be rationalized. I believe the situation is similar to this:

Some average Joe is convinced he is an awesome paper rock scissors player, and is addicted to the game. However he's not very good, he always picks paper. He likes to play $100 a game. You come along, play him, beat him for every penny he's got, and walk away. He happens to have a wife and children, and they are now homeless and in real bad shape. Who here thinks this is not wrong, however you define it?