User blog comment:XGlass Reflection/Ch. 48 Review~ OMG HE SPEAKS! *O*/@comment-76.31.149.155-20131005031938/@comment-179280-20131005040740

Because her obsession with Eren threatens an even bigger hope for humanity: Ymir (and all the secrets she must talk about). Even Hanji aknowledges how valuable she is, but Mikasa disregards this just because of her unhealthy obsession.