I didn't say we shouldn't care. I said we shouldn't judge.
Again, I'm taking a more general approach to this than just the situation at hand, but:
It seems to me that to care effectually, the very least that is required is to judge the perpetrator to have committed a wrong. To say, "I care that your family was massacred by some militant faction, but that's just part of their culture so I'm not going to judge them" is a particularly ineffectual caring. It is even more problematic if it is used as a justification not to interfere in order to prevent some future massacre. It seems to me that there can be no real line separating judgement and caring. In order to care that something bad has happened or is happening, we have to judge the behaviour that results in that "something bad" as being wrong. If we categorize the behaviour as wrong, then the actors must be doing something wrong, and we are thus implicitly stating that whatever reasons the actor might have (including cultural background) for that behaviour is insufficient to justify the wrong. In some cases, we might care more about preserving cultural autonomy than we do about the individuals harmed by that culture's practice, but in those cases I would still categorize it as a lack of any effectual type of care.
In any case, I am not sure if a cultural analysis would be entirely appropriate to apply to the situation in this thread (even though I am assuming it is a hoax), as cannibalism is not a cultural norm in China. If a community in Iowa took up ritualistic (and voluntary) human sacrifice, I don't think it would be appropriate to infer a cultural immunity to that when it should be clear from the laws of the US that such behaviour is unnacceptable, even though the victims volunteer and nobody in the community considers the behaviour to be aberrant.