I don't think it's just as obvious. Or, to me it is.. But I don't really think you can compare it to the parents-child-dead-thing. I have a really hard time with these things, comparing these things.. I tend to get confused when people try to explain why it's the same, because it (almost) never is. And there are different "rules" about everything, just like every time there is a different situation.
To me, you can't blame people for what they didn't really do, and didn't want anyone else to do, and didn't know anyone else could do because of what they did. But, like I said, it's different in every situation, but in the "Tara, Willow, Xander and Anya are killed all people The First killed"-situation.. I'd stick to the "theory" I mentioned above.