Frist, he said he wasn't joining because they wouldn't let him keep ownership of his prior work. They publicly announced that all developers were joining, forced him to make a decision quickly, and refused to negotiate. They in effect forced him out of his job. Him losing a game he built was not a "minor detail".
Second, he did not call Zynga evil because of that. His actual words: "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."
Politeness and grace do not require you to bend over and take it. They do not require you to shut up when your conscience insists that you speak.
That's not true. This is the reason he gave:
An evil company is trying to get rich quick, and has no regard for the harm they're doing along the way. It's not making things of value, it's chasing a gold rush. An evil game company isn't really interested in making games, it's too busy playing a game -- a game with the stock market, usually. It views players as weak-minded cash cows; and it views its developers as expendable, replaceable tools to create the machines that milk those cows.
For my part, I'll stick to working for employers with reasonable terms of employment.
Two important things to remember about negotiating contracts: A) They are mainly about the spirit of the agreement, and B) If any of the language actually gets as far as being tested in a court and you're just an individual, you're probably already fucked.
Zynga/OMGPOP clearly think it's unreasonable for any of their employees to do any outside game work. When Shay said, "Hey, can have an exception for my pet project," they said no. If Shay had tried to find some behind-their-back trick, the best case is that they just wouldn't care.
The worst case is that they fire him and bring a suit to take the game from him. Whether or not they win, Shay probably can't afford to spend $100k or more on a lawsuit, not for a little side project. So if he's lucky he escapes with $5K in legal bills so that he can hand the game over to him and agree in writing never to utter the word "Zynga" again.
Your approach might be enough to win a lawsuit. But he probably can't afford to fight a lawsuit, so whether or not he'd eventually win doesn't matter. Even if he could, it would be a hollow victory. He'd get to keep his modestly successful iPhone game, but it would cost him his job and maybe a year's salary on lawyers, plus 2-3 years of aggravation.
"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."
A better way to phrase it would be to say "Pierce's article says something impolite and ungraceful in the most polite and graceful way possible".