As new incidents happened today in London, we see how important is trust in the human society. We agree somehow to not hurt each other, and to cooperate for achieving goals. For my vacation I went to an office, I gave to the women there a plastic card (my credit card), received back a printed paper (my flight ticket). And I'm pretty sure at the date printed there a plane will be at the point indicated to fly me. This doesn't work if some people decide one day to blow themselfs up in a subway train. So we'll have to isolate these guys, and make sure that nobody comes to the conclusion that blowing himself up to kill others is something to do.
The chemistry of trust looks easy to decode, as described here, but the reality is far more complex.
Too much of what we accomplished relies on our cooperation, and trusting each other, so losing it is not an option.