Uber and Airbnb haven't just changed the world. They've made it better.

At least, that was the starry-eyed view that Uber CEO Travis Kalanick and Airbnb co-founder Joe Gebbia pushed during their talks during the second day of TED this morning. The two tech leaders, whose companies have faced frequent criticism and relentless opposition from regulators, reminded TED attendees not just how monstrously successful their respective businesses have been, but made the case that their success is actually good for the world.

Gebbia argued that Airbnb has compelled people to overcome their "stranger danger" bias and fear each other less. To demonstrate just how deep that fear can be, Gebbia asked everyone in the audience to unlock their phoness and pass them to the person to their left. As the sound of the crowd grew to a nervous rumble, Gebbia said, "That tiny sense of panic you're feeling right now? That's exactly what hosts feel the first time they open their home."

Then added: "By the way, who’s holding Al Gore’s phones? Will you tell Twitter he’s running for president?"

To show how Airbnb can uproot this deep-seated fear, Gebbia pointed to a study the company recently completed with Stanford University that measured people's willingness to trust someone based on various metrics like the person's age and geography. The study found that the more similar people are, the more willing they are to trust one another. But when you add reputation to the mix, as Airbnb does with its reviews, positive reputations yielded more trust than even close similarities.

"Design can overcome our most deeply rooted stranger danger bias," Gebbia said. For Airbnb, this message about trust and radical openess is crucial to undercutting the headline-generating stories about how Airbnb guests have trashed hosts' homes or been personally attacked by hosts.

In the same way, Kalanick sought to reinforce the idea that, by removing cars from the road, Uber is performing a critical public service. A future with fewer cars on the road, he said, improves people's quality of life and removes thousands of metric tons of carbon dioxide from the air of each city Uber conquers.

Kalanick took aim at regulations he saw as thwarting such progress and pointed to the jitneys of the early 1900s as proof of how history has gotten it wrong before. The jitney, Kalanick explained, was the original Uber, designed to take anyone anywhere they wanted to go for a nickel. The jitney experienced explosive growth, running nearly as many rides per day in Los Angeles as Uber does today. But within a few years, Kalanick said the entrenched trolley industry regulated jitneys "completely out of existence."

Sense a similarity? Kalanick's message was clear: had jitneys been permitted to operate unfettered by government oversight and unbothered by entrenched interests, maybe nearly a century later, we wouldn't live in a world in which one-fifth of carbon dioxide emissions come from cars; where humanity spends billions of hours a year sitting in traffic; and where cities are lined with parking garages, or, as Kalanick calls them, "skyscrapers built for cars."

But the jitney failed. So now, there's Uber. And now, Kalanick seems to be arguing, we face a fundamental choice between allowing history to repeat itself and allowing Uber to make history.