[nulbyte]

A manufacturer can choose what types of products it won't manufacture. Why can't a publisher choose the types of work it won't publish?

[dane-pgp]

Because the publisher is choosing to publish based on the identity or opinions of the customer.

To give another controversial example, there's a difference between a manufacturer choosing not to produce customized cakes, and a manufacturer choosing not to produce cakes customized for interracial couples.