Photo: Eric Risberg / Associated Press

The 61st floor of Salesforce Tower — the highest point you can get to over San Francisco without taking flight — feels heavenly.

Smiling baristas pour coffee. A pianist in a jaunty fedora plays upbeat tunes. The floor-to-ceiling windows offer stunning views of the city’s older, more established sights: the Transamerica Pyramid, the Golden Gate Bridge, Alcatraz.

From up here, you can’t see the hellish landscape for which the city is becoming equally well known. The people jabbing needles into their necks, the tent camps, the piles of trash and feces. They’re out of sight from this perch, and you could easily pretend they don’t exist.

But Salesforce chief Marc Benioff won’t pretend. In fact, he won’t stop talking about that other San Francisco, the one that can’t even be called an underbelly anymore because it’s so out there and so in your face when you’re not high up in a tower. Benioff will tell anybody he encounters that what’s needed to finally fix the homeless crisis is the passage Tuesday of a tax on Salesforce and other big companies.

Benioff really, really, really wants Proposition C to pass. But why?

“From here, it’s beautiful,” he said, as we talked on the Ohana Floor, the name Salesforce gave the tower’s top floor — it’s Hawaiian for family. “We’re looking at Mt. Diablo from this window, but the reality is if we went down on the streets, it would be a horror show, and that has to come to an end. I think it’s extremely embarrassing.”

It was embarrassing, he said, that when Jim Cramer, the host of CNBC’s “Mad Money,” interviewed him the other day about Prop. C, Cramer told him about seeing what he said was a homeless man rob a cashier at knifepoint at a San Francisco Walgreens and the cops telling him the assailant would be back on the streets in a couple of days.

It’s embarrassing that some of the 170,000 people attending Dreamforce, his company’s annual September conference, emailed him to complain about the homeless problem and filthy streets. But mostly, he said, it’s embarrassing that in a city with 70 billionaires, there remains poverty so stark that public schools count more than 2,000 homeless children among their students.

“It’s a crisis of inequality,” he said. “It’s a crisis of inaction. It’s a crisis of indifference.”

Prop. C would raise the gross receipts tax an average of 0.5 percent on the 375 companies in San Francisco that bring in more than $50 million a year and would apply only to their revenue above $50 million. It would raise $300 million annually for supportive housing, mental health and drug treatment services, and more shelter beds and hygiene centers.

Mayor London Breed and other opponents of Prop. C say throwing more money at the problem isn’t the answer and that there needs to be better accounting of the money San Francisco already spends. But Benioff says the crisis demands an immediate injection of major funds, before our city and its business community is lost for good.

“You have to ask the question — if things get really bad with homelessness, am I going to have Salesforce in San Francisco?” he said. “The homeless problem is becoming bad for our business, and that is why we are getting involved and taking action.”

The measure was chugging along, not much noticed inside the city, let alone outside it, until Benioff declared his support on Oct. 8. He has personally given $2.02 million to the Yes on C campaign, and his company has given an additional $5.88 million. That is believed to be the most ever spent on a local San Francisco campaign in its final weeks. The campaign has so much money to spend so rapidly, it’s even putting up billboards outside San Francisco.

Jess Montejano, a spokesman for the No on C campaign, said his team doesn’t expect the outcome to be much different than it did before Oct. 8, though he wouldn’t say what that predicted outcome is.

“Election day will tell the final story, but we believe that Marc’s multimillion-dollar investments failed to effectively move the needle to earn the broad support that this measure needs,” he said.

Most observers expect Prop. C to win the majority of votes and pass, but not achieve the two-thirds support it would need to prevent a likely lawsuit by those who believe that level is required under state law.

Perhaps determined to surpass that two-thirds mark, Benioff is appearing on every national news network to talk up the measure, tweets about it constantly and gave a long, rousing sermon-like speech written by a former Obama speechwriter to a packed crowd of businesspeople and politicians at the annual SPUR lunch Tuesday.

He had two tables at the luncheon, with seats reserved for Jennifer Friedenbach, the director of the Coalition on Homelessness, and progressive supervisors and Prop. C supporters Jane Kim and Aaron Peskin — not exactly the types you’d imagine breaking bread with a tech titan. But nothing about Benioff — Forbes once described the 6-foot-5 billionaire as having “the mind of a fox and the body of a bear” — is predictable.

Until recently, he didn’t talk much about other CEOs and their philanthropy, or lack thereof, but that changed big-time when he got into a Twitter squabble about Prop. C with Twitter and Square CEO Jack Dorsey.

“That’s been manna from heaven,” Benioff said with a smirk, noting the national and international media took note of Prop. C once it became a battle of the tech billionaires.

He said he simply doesn’t buy the claims of Dorsey and others who oppose Prop. C that the tax would harm their businesses and, in the case of Square, perhaps lead to a departure from San Francisco altogether.

“I don’t believe their accounting,” Benioff said.

I asked for comment on his charges from Twitter, Square and Stripe. Twitter and Stripe declined.

A Square representative said, “We are not opposed to a tax increase. We are opposed to a tax increase that could result in Square paying twice as much as Salesforce, which is four times larger than Square. We just want to be treated fairly compared to our peer companies.”

One little-known inspiration for Benioff’s determination is his maternal grandfather, Marvin Lewis, who was a San Francisco supervisor from 1944 to 1955. He was credited with championing the creation of BART and backing the “pedestrian scramble” — the traffic signals that allow walkers to cross an intersection in any direction while cars wait.

Photo: Courtesy Moulin Studios

Lewis was also an advocate for the homeless and showed a short movie about the problem in SoMa at a Board of Supervisors meeting. A 1953 Chronicle article about it read, “According to the supervisor there are many persons, including children, forced to live in sub-standard dwellings, just a few blocks from the city’s finest shopping district.”

By the time Benioff was born, Lewis was working as an attorney on Market Street. He was best known for representing a woman who claimed she became a nymphomaniac after a cable car accident. The media called the 1970 case “The Cable Car Named Desire.”

But Benioff most remembers visiting his grandfather at his offices and walking around Mid-Market with him, handing out $20 bills to homeless people.

“Maybe it’s in my subconscious somewhere. Maybe I’m just channeling my grandfather,” he said. “He always told me to take care of people who are less fortunate than myself.”

So would he follow in his grandfather’s footsteps and run for political office, a goal some observers say must be the point of his Prop. C proselytizing?

“I would never run for political office,” he said. “I really believe, exactly as I’m trying to demonstrate, that business is the greatest platform for change. ... My goal is to demonstrate that businesses can be this kind of force for good in the world — that we can do well and do good.”

Prop. C is trying to do good. Whether it’ll do well with voters, we’ll find out Tuesday night. And you can be sure a certain billionaire will be watching.

San Francisco Chronicle columnist Heather Knight appears Sundays and Tuesdays. Email: hknight@sfchronicle.com, Twitter: @hknightsf