At the same time though, he would be being asked to go against his beliefs. If I am not mistaken, when Shawn (HBK) came back as a Christian, they didn't demand he continue the "sexy" act. Then again, he likely meant more to Vince than CM Punk. Either way, anyone who is willing to sell out their own beliefs is a coward in my book. Paycheck or not.
I'd have to say that's a faulty analogy. HBK not playing the sexy boy character because he is a Christian is the trait of a persona that WWE controls exclusively. It is completely a character that is owned and promoted by WWE and HBK solely for the benefit or detriment of HBK and WWE.
WWE has a working partnership with Susan G Komen. It is a business relationship and the actions of the parties in the relationship are all affected by all parties. While Punk is under contract he can be under an agreement to not say or do anything that would cause detriment to any working partners of WWE. If so, he would be unable to speak out against them at any point of time while under contract or face penalties and even legal consequences for it... this is not an unusual situation in an entertainment or sports company. If Punk were to say these things about Susan G Komen while under contract to WWE, not only he but also WWE could have faced legal consequences if the comments were found to be detrimental to Komen. And it's not a matter of freedom of expression either. A binding contract can override your freedom of expression since it is signed willingly.
An example of limits of freedom while under contract is not unusual. For example, even in their own free time, basketball players are forbidden from speaking negatively publicly about the referees. They could be fined. Another example is David Wells, who had a book ghost written about himself where he claimed to be drunk while pitching his perfect game for the New York Yankees. Now, the book was actually written while Wells was not a Yankee, published when he was and Wells was legitimately fined $100,000 because it violated his contract that he would not express any opinions that were detrimental to the Yankee organization.
So WWE forcing or not forcing HBK to act in one way affects no one but WWE and HBK. Forcing their wrestlers to support an entity that WWE is partnered with affects a lot more than just WWE and their wrestler. And that is why the analogy does not work.
Now personally, I agree and would never put myself in a situation where I had to say one thing while believing another thing. I think my personal dignity is much more important than the money. However, I am not Punk and I did not sign a huge contract with a company that likely severely limited my right to express myself however I want.