Open societies are always endangered. This is especially true of America and Europe today, as a result of the terrorist attacks in Paris and elsewhere, and the way that America and Europe, particularly France, have reacted to them.

Jihadi terrorist groups such as Islamic State and al-Qaida have discovered the achilles heel of our western societies: the fear of death. Through horrific attacks and macabre videos, the publicists of Isis magnify this fear, leading otherwise sensible people in hitherto open societies to abandon their reason.

Scientists have discovered that emotion is an essential component of human reasoning. That discovery explains why jihadi terrorism poses such a potent threat to our societies: the fear of death leads us and our leaders to think – and then behave – irrationally.

Science merely confirms what experience has long shown: when we are afraid for our lives, emotions take hold of our thoughts and actions, and we find it difficult to make rational judgments. Fear activates an older, more primitive part of the brain than that which formulates and sustains the abstract values and principles of open society.

The open society is thus always at risk from the threat posed by our response to fear. A generation that has inherited an open society from its parents will not understand what is required to maintain it until it has been tested and learns to keep fear from corrupting reason. Jihadi terrorism is only the latest example. The fear of nuclear war tested the last generation, and the fear of communism and fascism tested my generation.

The jihadi terrorists’ ultimate goal is to convince Muslim youth worldwide that there is no alternative to terrorism. And terrorist attacks are the way to achieve that goal, because the fear of death will awaken and magnify the latent anti-Muslim sentiments in Europe and America, inducing the non-Muslim population to treat all Muslims as potential attackers.

And that is exactly what is happening. The hysterical anti-Muslim reaction to terrorism is generating fear and resentment among Muslims living in Europe and America. The older generation reacts with fear, the younger one with resentment; the result is a breeding ground for potential terrorists. This is a mutually reinforcing, reflexive process.

The hysterical anti-Muslim reaction to terrorism is generating fear and resentment among Muslims in Europe and America

How can it be stopped and reversed? Abandoning the values and principles underlying open societies and giving in to an anti-Muslim impulse dictated by fear certainly is not the answer, though it may be difficult to resist the temptation. I experienced this personally when I watched the last Republican presidential debate; I could stop myself only by remembering that it must be irrational to follow the wishes of your enemies.

To remove the danger posed by jihadi terrorism, abstract arguments are not enough; we need a strategy for defeating it. The challenge is underscored by the fact that the jihadi phenomenon has been with us for more than a generation. Indeed, gaining a proper understanding of it may be impossible. But the attempt must be made.

Consider the Syrian conflict, which is the root cause of the migration problem that is posing an existential threat to the European Union as we know it. If it was resolved, the world would be in better shape. It is important to recognise that Isis is operating from a position of weakness. While it is spreading fear in the world, its hold on its home ground is weakening. The United Nations security council has unanimously adopted a resolution against it, and the leaders of Isis are aware that their days in Iraq and Syria are numbered.

Of course, the outlook for Syria remains highly uncertain, and the conflict there cannot be understood or tackled in isolation. But one idea shines through crystal clear: it is an egregious mistake to do what the terrorists want us to do. That is why, as 2016 gets underway, we must reaffirm our commitment to the principles of open society and resist the siren song of the likes of Donald Trump and Ted Cruz, however hard that may be.

• Copyright: Project Syndicate, 2015