When one joins the military, I think there's an implicit understanding that putting on a uniform means you are accepting that you become more or less a walking target. Theoretically, you're putting yourself between the civilians of your country and its enemies. I appreciate the burden that those in uniform take up, even as I am often dissatisfied with the execution.
That's all the more reason that targeting civilians is just over the line. Especially in yesterday's case, it accomplishes nothing. As has been pointed out, the British are experienced in living with violence, far more than we in the U.S.
Even while my sympathies go out to those affected by this and other violence, I'm certain that their strength and resiliency will come through.