This is a flawed argument. If you were to never make your bet in the first place, the "person who can't stop gambling" would still be losing their money to the bookie. You're not enabling the bookie taking their money.

In fact, if you're winning more than you're losing, you're decreasing the profit of the bookie. You are therefore making it a less worthy venture for them to hold these ethically-negative gambling events. If you were to win enough, the bookie would lose money from the venture, eventually resulting in them no longer hosting gambling events.

So actually, winning money off of bookies is an ethically good behavior, since it's negative feedback for them enabling other gamblers with "uncontrollable behavior" to lose their money.