I know why...!
You know how I said I was frustrated with Dean being so hardheaded about the visions? I know why, now, and it makes me feel a bit better.
DEAN: If you're as bad as they say you are, why haven't you hurt me?
DARKNESS: For the same reason you will never hurt me. We are bound, Dean. We will always be bound. You helped me. I helped you. No matter where I am, or who I am, we will always help each other.
I think Dean is avoiding the issue of the visions because it means danger to Amara. He instinctively/unconsciously feels the danger of going down that path. And the danger is not necessarily for Sam (although he argues that point convincingly). The danger is for Amara. We've seen Dean protect the baby Amara in Episode 1 and 2, without knowing that she was the Darkness. Of course, it can be argued that this is because she is a baby, but the fact that he was willing to shoot his way out of the hospital before Sam stopped him is important, I think, as well as what The Darkness said here to him. Whatever the case, I think Dean is going to be choosing the path that protects Amara, without him even knowing he is doing it.
DEAN: If you're as bad as they say you are, why haven't you hurt me?
DARKNESS: For the same reason you will never hurt me. We are bound, Dean. We will always be bound. You helped me. I helped you. No matter where I am, or who I am, we will always help each other.
I think Dean is avoiding the issue of the visions because it means danger to Amara. He instinctively/unconsciously feels the danger of going down that path. And the danger is not necessarily for Sam (although he argues that point convincingly). The danger is for Amara. We've seen Dean protect the baby Amara in Episode 1 and 2, without knowing that she was the Darkness. Of course, it can be argued that this is because she is a baby, but the fact that he was willing to shoot his way out of the hospital before Sam stopped him is important, I think, as well as what The Darkness said here to him. Whatever the case, I think Dean is going to be choosing the path that protects Amara, without him even knowing he is doing it.