Why would a christian bakery sell gay wedding cakes?

The truth is, there is already plenty interference is private business, but it (seems) to not be evenly applied. If I request a library stock (or borrow) a book that I'd like to read, I don't consider political aesthetics to be a valid reason to refuse.

> I'm sure there are plenty of Christian book stores / libraries out there who are unwilling to stock The God Delusion

Do you mean a normal bookstore owned by Christians, or a specialist bookstore that only stocks christian literature? If the store could refuse any non-christian material (e.g. a cookbook) as well as Dawkins books, I'm not sure if that's censorship - a greengrocer can also refuse to stock The God Delusion on similarly reasonable grounds.