SAN FRANCISCO — It sounds sinister. A soft-spoken cryptocurrency mogul is paying for a private network of high-definition security cameras around the city. Zoom in and you can see the finest details: the sticker on a cellphone, the make of a backpack, the color of someone’s eyes.

But in San Francisco, a city with a decades-long anti-authority streak, from hippies and pioneering gay rights activists to the techno-utopian libertarians and ultra-progressives of today, the crypto mogul has found a surprisingly receptive audience.

Here’s why: While violent crime is not high in the city, property crime is a constant headache. Anyone who lives here knows you shouldn’t leave anything — not a pile of change, not a scarf — in a parked car. Tourists visiting the city’s vistas like Twin Peaks or the famously windy Lombard Street are easy marks. The city government has struggled to solve the problem.

In the middle of this is Chris Larsen, a 59-year-old tech industry veteran, paying for hundreds of cameras. He sees it as an alternative system of urban security, and he hopes it becomes a model for other cities.

This just may be the best moment for him to explain why a rich guy paying for surveillance cameras all over a city is not a terrifying invasion of privacy. Around the country, Black Lives Matter movement protests have led to a reckoning on policing and how it should be done. Many of the activists leading this movement are fighting to abolish or defund — reduce funding for — police departments. Last week in New York, for example, the mayor announced the police budget would be cut by $1 billion.

In San Francisco, where many locals push for this kind of police reform, those same locals are tired of the break-ins. So how do they reconcile “defund the police” with “stop the smash and grabs”?

Mr. Larsen believes he has the answer: Put security cameras in the hands of neighborhood groups. Put them everywhere. He’s happy to pay for it.

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First, let’s state the obvious reason — besides privacy concerns — that Mr. Larsen’s plan might be viewed with suspicion: He’s in tech.

Longtime San Francisco residents and the tech workers have not historically seen eye-to-eye on many things. The natives resent the private tech shuttle buses and the spiraling cost of living brought on by the new arrivals. They even resent their housing aesthetic: Glass and metal and pretty Victorian houses now painted in shades of black and gray.

But here’s where it gets more complicated: Privatization is hardly a new thing in the city. Around a quarter of San Francisco parents send their children to private school, a higher percentage than many large cities, including New York. Private security officers are a common sight. Plenty of people already have security cameras pointing toward the street. So would a privately owned camera network be so out of bounds?

And Mr. Larsen is no tech carpetbagger. He grew up in a middle-class family in the Bay Area. His father worked the night shift as a mechanic at the San Francisco airport. In 1984, he graduated from San Francisco State University, and he is now a major benefactor, donating one of the largest gifts the school has ever received. He also has been a longtime advocate for privacy, cofounding the coalition Californians for Privacy Now to help pass a 2004 privacy bill, California S.B.1, commonly known as the California Financial Information Privacy Act.

In 1997, Mr. Larsen co-founded an online lending company called E-Loan, which went public two years later, and he stayed on as chief executive until 2005. In 2012, he co-founded a start-up that would be called Ripple, which helped people send money online using so-called blockchain technology and the digital token called XRP. During the peak of the speculator-crazed crypto boom of 2017, its value spiked wildly. Mr. Larsen became one of the few crypto entrepreneurs to make and then hang onto that overnight fortune.

His apartment on Russian Hill has a trophy view of San Francisco Bay and the tight curves of Lombard Street. But also: the crews coming in to rob tourists’ cars, right in the middle of the day. Mr. Larsen watches the police drive by, and the criminals arriving 15 seconds later, smashing the vehicles’ windows and stealing luggage.

“They don’t care at all — they don’t care if they’re being seen,” Mr. Larsen said. “It’s brazen.”

His father-in-law’s car was robbed. Mr. Larsen’s own car windows were smashed. When a group of men climbed into his garden and one of them cut the wires on his home security system, while his children were sleeping inside, Mr. Larsen decided that he had had enough.