I guess it's a question of how high that cost can go before it becomes no longer worth it.
The comparison kromo makes with bees does look rather tactless but all the same I think it's an important point. Terrorist attacks are by their nature more dramatic, and more noticeable, but they also remain a comparatively very, *very* low risk, even after the three recent attacks this year. I'm not for a second saying that it's an acceptable risk, and of course we have to work to minimise that risk as far as possible, but we still shouldn't be exaggerating the scale of the risk. Remedy sometimes worse than the disease, and all that.
The nature of the two London attacks, too, seems to be so frighteningly random as to leave me wondering if there's anything meaningful that can be done. All the attackers had to do was to get in a car and drive it really fast into people. I'm not sure that takes a lot of planning, really. At least these people were on the watch list again, as I understand it. Whether that is a comforting thought, or one that just adds to the weight of frustration at the apparent inability the Security Services have to stop all these attacks, I don't know.