I actually have no problem with any of this. They're just making a product for people to enjoy. Just because they're running data sets, tests, and using social "science" (bah) to maximize products... so what? What makes that worse than building a product based on your intuition that happens to appeal to people as well on these lines?
I think Zynga is a foul company. I think their product has a net societal cost, and I think the crap they pulled on some of their employees prior to IPO is unconscionable. But I think this aversion to using psychology to optimize your product is misplaced. Nobody is getting hypnotized here. They are just using every tool in their arsenal to make their product perform as well as possible. They do this in an unashamedly metric-based way. Every product you encounter in life attempts to influence and manipulate you. The scientific approach just happens to be very good at optimizing processes.
Last point in this rant... I do believe Zynga makes most of their money off the weak and the crazies who will put thousands of dollars they can't afford into their farmville farm. I do believe that is morally repugnant, and it's well within their power to stop that (which I'm sure they'll never do). I just don't think the design of their games is an issue... it's their billing.