As often as not - and the 9/11 threads were a case of this - people post here on these kind of threads not as a way of registering outrage, but as a way of trying to deal with the shock felt by coming up against terrible things.

It's rather the same way as when your are together with friends in the wake of some terrible event, you want to talk about it. That's not a matter of making a public protest, it's a way of dealing with your own feelings, and trying to make sense of them.