Fernando Henrique Cardoso in openDemocracy:
Sergio's entire life was dedicated to the ideals of human rights and humanitarian work. For him freedom and human dignity were the foundation of peace and justice. Sergio was courageous and compassionate. Bold but also pragmatic. Often at the frontlines but always taking the side of the weak, the vulnerable, the powerless. Uncompromising in his principles but with a gift for listening to and learning from those he worked with. He had the capacity to combine a maximum flexibility in dealing with the complexities of real life situations with a strong commitment to basic values. This allowed him to stand unequivocally on the side of the victims while talking to all the parties involved. Perhaps this is as close as one can get to being a practitioner of what I would call the art of politics: this combination of vision and pragmatism, flexibility in the means and consistency on the goals.
From Cambodia to Bosnia, Rwanda to Kosovo, East Timor to Iraq, Sergio came to grips with some of the most dreadful conflicts of the last decades. Time and again he was confronted with life and death questions for which there were no easy answers. How to balance the obligation to protect the victims with the denunciation of human rights violations? What kinds of compromise are or are not acceptable to minimize human suffering? At what point pragmatism becomes complacency in the face of the unacceptable? When is dialogue no longer an option and the aggressor has to be engaged despite the risk that, in the short term, the level of violence may increase? How to define this moment in which, faced with massive human rights abuses and crimes against humanity, it is legitimate to use force in the pursuit of peace?