If the argument is that there is something immoral about them charging people for use of their subscription service, I call bullshit. Until incredibly recently, they had no subscription service. Now they are offering the _option_ to use a subscription service. If you find the fees are too high, you are not obliged to take part in it. I think the real reason this upsets so many is that it clearly is worth it for many developers to take part in it, just like it clearly is worth it to let apple take their 30% cut for everything else sold on the app store. People are riled because they don't want to have to pay apple this fee, but hard cold business logic demands that they should, because it is profitable to do so (or less unprofitable than not doing so). It wouldn't be threatening at all if you felt like you could afford to just walk away from the ecosystem apple's built.
Which seems to indicate they are adding value.
Now, as to whether the value added == 30%, I direct you to the first paragraph. But what's the motivation to create such a wonderfully easy to use ecosystem if you can't derive a profit off it?