I think you are wrong and it has everything to do with free speech. Same as my owning a Gun is free speech. Now if you not getting the message then its not my fault.
What about the freedom to burn books? The government isn't censoring Harry Potter. If someone wants to exercise their freedom to burn a book, why isn't that free speech? The ACLU and most liberaltarians favor flag burning, but are whining about this pastor's freedom to make a statement about Harry Potter.
Are you implying this pastor shouldn't have the freedom to burn any book he sees fit, so long as he pays for the book?