At a summer school, organised a few weeks ago by the Alliance of Civilizations, which brought together over 170 young people, from 70 countries, all participants were invited to summarise the week's experience in one word. Everyone was ecstatic and used sparkling words - a once in a lifetime feeling; love; hope; unique; accomplishment; peace and the like. One participant, showing a little more reserve than the rest in that euphoric atmosphere, chose the word "possibility", a statement that has resonated quite dramatically in recent events which show how right her caution was.

The indignation that has flared up in so many countries against a provocative video, produced in murky circumstances and aimed at offending one group's religious beliefs, is legitimate and fully understandable. No believer, be they Muslim, Christian, Jewish, to mention only the religions of the Book - is ready to accept indecent attacks on matters they hold sacred. All citizens should have the right not to be gratuitously offended in their religious feelings and aspire to be protected against such indecent attacks. But as a right, it should be claimed in a lawful, peaceful way within the bounds of the law.

At the same time, while we hold this right, it is important to recognise that one person's contemptible actions do not represent an entire nation, or everyone in a particular group or of a certain faith. Here, I must emphasise the crucial responsibility that falls on political and religious leaders to speak out to their constituencies, urging them to be mindful of this fact.

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Apart from all this, what is entirely a separate matter and must be seen as such, is the legitimate manifestation of anger being instrumentalised by extremists to foment mob violence for their own political ends. In my view, the brutal killings in Benghazi had little to do with the release of the video. The perpetrators of this vicious terrorist attack have to be brought into justice as the Libyan authorities promptly pointed out. But in the same way that extremists do not represent all Libyans, the makers of the offending video don't represent America, all Americans, or all Christians. In my mind, it is necessary for those of us in the middle - the overwhelming majority - to take back the conversation from the extremes and occupy our rightful place in it.

Another concerning fact is that there seems to be a primordial angst that is all too easily exploited when events like this happen. The air is ripe, for those so inclined, to take advantage of popular sentiments, rouse people and encourage violence to strengthen their positions of power. While this brings me back to my earlier point about responsible leadership, it also highlights the need to do deep thinking about the persistent tensions between the East and the West; about the bad relations between Muslim and Western publics with both sides holding negative stereotypes of the other; and how a tremendous level of hostility and animosity is ever present that needs only the slightest prodding to explode. It is ultimately an indication about how much the Alliance of Civilizations is a timely and rightful UN initiative, but is also a painful reminder to me that our work at the Alliance is far from done.

We must redouble our efforts to bridge cultural divides, promote cross-cultural understanding, trust and mutual respect among and within societies, at all levels - international, regional, national and local - and fields of action - from education to youth and media.

In democratic societies and increasingly all over the world, people are free to voice their rights. Let's join all our voices and work together to address in an appropriate way the alarming rise of extremism, religious hatred and hate speech, all of which undermine people's expectations of a better life in dignity, freedom and security. We need to be bold and take action urgently to turn the possibility of living together in diversity, dialogue, respect and peace into reality.

Jorge Sampaio is the United Nations High Representative for the Alliance of Civilizations, and the former president of Portugal.