It's just like Facebook has porn patrol.
Being a vendor of a product isn't just about moving product, it's about moving product in a direction that you believe makes the world a better place for you to live. Apple has the right to choose how to let people use their platform.
Imagine a world where you have no right who you can and cannot sell your hard work to. Those signs that say, "We have the right to refuse service to anyone" -- all those would have to come down, by law!
I think, right now, that I would prefer a world where a vendor of a service can decide who it does and does not provide that service to than a world where the builder of a product or provider of a service does not have that right.