Members of parliaments everywhere have been asked to "stand together to stem the poisonous rising tide of fear and hate that breeds division and extremism".
We all need to hold ourselves to this same challenge. It feels like the world is entering a frightening new phase. No one and nowhere is immune.
A lifelong cause
Cox dedicated her life to the struggle against injustice and intolerance. I did not know Jo myself, but so many across Oxfam did and were touched by her.
So many people were inspired by her compassion, commitment and energy for change. She was clearly an incredible woman.
Jo was a passionate feminist, a woman after my own heart. While working in Oxfam she got involved in a discussion about how women can best become genuinely empowered.
"Education", said one person. No, said Jo, the answer is politics. Support women into political power and the rest will follow. Everything I have ever experienced - working with women in Africa and across the world - tells me she is right.
Jo may have been killed because of her views. She is not alone in having paid that price.
On average, three to four people are killed each week defending their lands. A few months ago in Honduras, for example, Berta Caceres, a community leader, was shot dead in front of her children for defending her community's land rights, having been threatened for years by big business interests.
On average, about 70 journalists are killed each year simply because they are journalists. Women are murdered just for being women, such that we had to invent a new word for it, "femicide", 40 years ago.
In the United Kingdom alone, hate crimes reported to the police rose 18 percent last year to 52,528 - and 82 percent for race hate, 11 percent for sexual orientation hate, 6 percent for religious hate (PDF).
Carefully manufactured hate
This is a global pattern. The mass kidnapping of girls in Nigeria, the murder of tourists on a Tunisian beach, of Parisian concert-goers, the shooting of 49 gay men and women in Orlando - the murder of an MP in a small English town - are among countless examples of hatred unleashed.
This hatred is by carefully planned manufacture. Fearful, hate-filled arguments are winning people's favour, but they are being stoked by those without any interest in ordinary people.
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The rules of acceptable behaviour in society have been mangled towards isolationism, greed and intolerance.
The core values of humanity, as reflected in international law on human rights and humanitarianism, particularly refugee rights at the moment, have been undermined by rich and powerful interests.
Across the world, politicians are playing fast and loose with myths and lies to further their short-term agendas. This is eroding trust and tolerance in our societies.
We have experienced this time and again in Africa, where politicians have whipped up hatred and fear with no care for the cost. The wounds from genocide have not healed and Africans are still dying every day in conflicts fanned by ethnic hatred. Media owners reward pit-bull journalism to sell fear.
Researchers craft arguments to justify economic extremism. Religious messages are warped. Guns and bombs are allowed into the hands of radicalised minds, with predictable consequences.
I think that we feel less safe now to speak our views and stand our ground. No matter which side of the argument one is on, tolerance is in short supply.
No woman or man should be threatened for holding peaceful views, whether these views are from those you agree with or those you don't.
Defending hard-won freedoms
What can we do? Tolerance comes from respect, from a feeling that those opposed to you are at least as valuable as you, as people.
This is not something that is granted or ceded. It is won by struggle. Fighting racism, tribalism, discrimination and xenophobia means to actively challenge it as unacceptable.
It is won at home when you talk to your children, when you engage with adults especially women, through to public mobilisation and voting at the polls.
Sometimes it might feel uncomfortable, sometimes dangerous. For some, life-threatening. But it is necessary if we want to stop asking ourselves what we have become.
It is easy to laugh or shrug off today's demagogues, thinking that our values of tolerance and security are somehow immune, that we can't slide backwards. Nothing could be further from the truth.
Each generation is responsible to defend and renew hard-won freedoms, and extend them to those people who have never had them.
I am proud to be part of that fight, and to work with so many who have been touched by Jo's desire for a better world free from the hatred and racism that killed her.
We must actively reject hateful ideology from all corners. We must support communities everywhere to replace it with a culture of peace and tolerance based upon social justice.