It's not predatory and unethical and it shouldn't be illegal. You can't point to any harm done because there is none.
I support the right of corporations to pick the business model that they feel is most appropriate to their game. If the gameplay was bad and I wasn't having fun then I would complain about that, but I have had fun so far and I haven't played enough to form any real criticisms yet.
I certainly won't complain about the fact that some people have put a lot more time or money into the game and that makes them more powerful. I'm happy for them, not jealous or envious.