See my #88.
There are other fantasy worlds depicted by a host of authors that Ratzinger does not pick on. He picks on this one.
He sees a difference. I think he rejects this particular fantasy world because it is TOO close to what an occult world would look like....which is why he says it BLURS the lines between (geweltshaung?) the worldview level good & evil.
That's my take on interpreting what he's saying. It's hard to get to specific without knowing specifically what he has problems with.
But, he did not ~actively~ pick on Harry Potter. He was asked to comment. Which he did.
Very briefly.