Apple is, and should be, free to prohibit any content they want on their store.
Absolutely!
It's their store, we shouldn't force them to add stuff they don't want.
Nobody is forcing anything. Yet. For the same reason that Apple has a right to carry (or not carry) whatever they like, I have the right to complain about it.
The problem here is the locked down devices. You have no other way of installing things on an iPhone.
And this is the reason I'm actually alright with forcing Apple to carry certain things that they might not otherwise want to carry. If the App Store rules weren't such a moving target, I'd have less of a complaint, but the fact that limitations on what software I can install on my device are added after the initial purchase of my device is a bit of a problem, at least to me.