From his article, Zynga isn't evil because of the minor detail in the contract. He gives a reason why he thinks zynga is evil and so not worth negotiating this minor detail.

"When an entity exists in an ecosystem, and acts within that ecosystem in a way that is short-sighted, behaving in a way that is actively destructive to the healthy functioning of that ecosystem and the other entities in it (including, in the long term, themselves) -- yes, I believe that that is evil. And I believe that Zynga does exactly that."