I don't know if I would buy the whole 'defense mechanism' argument. What may be going on may be similar mechanically, but isn't just a 'defense mechanism'.
When someone you care about (I use a broad definition of 'care about' here) are in a bad situation, you can recognize that. You can think to yourself about how that would be undesirable, about how that person is likely unhappy, and perhaps question what you could do to supply relief to them.
The difference between those of us on the spectrum and those who aren't, is that we can consciously recognize those thought patterns. In addition, we can still continue to think, decide, contemplate, act, etc. outside of the control of any emotions those outside circumstances may provoke.
So, I don't think, it's so much that you're not caring, it just doesn't affect you at your root level like it does someone outside of the spectrum. So yes, it feels faked, but is there any difference, on the outside, between someone who reacts instinctively to tragedy and someone who contemplates it unemotionally and then acts in the same manner as the former?
It's a good question.