You're searching for the 2005 web-original short story Roger Williams, “The Fifth Gift”. This link points to a full text copy of the short story on the web..
The outline of this story is aliens giving a series of five amazing technological gifts to humanity, with enough pauses between them for humans to confirm that the gift is helpful. The first gift is a replicator that lets people make any number of copies of each alien device. The second and third gifts are unremarkable. The fourth gift protects a human from all kinds of harm, so by wearing it as an amulet, a human can take a spacewalk without a spacesuit.
However, the first four gifts don't get to their intended recepients. A secret agency collects the gifts all to itself, and kills every other witness, so instead of helping humanity prosper, they'll all rot in some government storeroom like the artifacts in Indiana Jones. The story is written from the point of a reluctant researcher who the secret service forces to examine the gifts.
It is the fifth gift that you seem to remember. When that one was activated, all humans suddenly became emphatic and started to care about other humans. (The alien gadget has turned humanity into Gaia from Asimov's Foundation's Edge, in five seconds after its activation.) Since the secret agency was led by humans, this led them into releasing the gifts for the benefit of mankind.
As the field established itself it overshot, and for one bright moment it seemed that I was sharing the thoughts of every single human being on the planet. I could sense Jones and Smith outside the door, reeling from the same sense I was. Further afield was a dim murmer, except for people I had some connection with. I could feel the friends I'd abandoned, who were suddenly aware of me as I was of them. In that moment we knew everything about one another, and I knew that if Smith and Jones [secret agents] recovered their wits they'd all be killed, and my friends knew that too, and they forgave me.
Somewhere in the Middle East a man was riding the subway with twelve pounds of explosive strapped to his body and a trigger in his pocket. He had been clutching the trigger, playing with it, steeling himself for his final act in the war between his people and their oppressors. But now he left the trigger alone, and when the doors opened he left the train and returned to the world. Out in the open air of a nearby park he would unwire and take off the explosives.
Deep in a London slum a room was filled with torpid bodies which suddenly, quietly awakened. The heroin was no longer at work in them, but neither were they now addicted. They looked around with dawning expressions of horror and hope as if to ask, "What the hell am I doing here?"
I must thank Zefram who pointed me to this remarkable short story in a mailing list post in 2010, following the tradition that the announcement for any new release of perl (a software package) comes with a literary extract.