Did you ever stop to consider perhaps money isn't the worst fallout? The families of addicts suffer as well–and I suspect, when we look back years from now, we'll see a pattern of spouses and children ignored & damaged because companies like Zynga analyze/optimize everything in order to maximize engagement. A single person can't compete with that.
You're not just engineering people to part with their money–you're using your skills to get them to part with their time.
Sorry, but I consider what you do (& Zynga does) unethical.