Vance Maverick points down at the pavement with a chuckle. There on the concrete, close to the spot in San Francisco’s Mission District where the 42-year-old Google engineer catches a private commuter bus to Silicon Valley, is some faint political graffiti. It’s still possible to make out a crudely painted Google search box; before it faded, Maverick explains, the search terms read: “Trendy Google professionals help raise housing costs.”

It’s safe to say that sentiment still holds. In the Mission and across San Francisco, long-time locals are disturbed by the profusion of young, rich tech professionals moving into their neighbourhoods, driving up house prices and – inadvertently or not – driving out residents. The phenomenon has inspired impassioned essays in San Francisco magazine, the London Review of Books and The New Yorker.

The Google buses, which often stop in spaces supposedly reserved for public transport, are a particular point of contention. This growing fleet of unmarked luxury coaches carries some 14,000 people on their 35-mile trip from the city to Silicon Valley and back. Since the search giant introduced the buses a decade ago, Facebook, Apple, eBay and almost 40 other companies have followed suit. Each new route quickly becomes a corridor of hip clothing stores and restaurants.

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Maverick admits that the criticism has upset some of his younger colleagues. “I’m old enough not to be personally offended, but I know some people at Google were surprised and hurt,” he says. “I’ve always found the graffiti amusing. It reflects the adversarial culture of public protest in San Francisco – which is part of the reason we’re all moving here.”

Yet campaigners say this culture is dying – that the home of the Beats and the hippie movement, and heart of the gay community, is fast becoming a vanilla monoculture made up of wealthy tech yuppies. Nowhere is this more true than in the Mission, traditionally a cheap, diverse area where middle-class families, working-class Latinos, struggling creatives and small businesses all rubbed along together. Now, it’s where Mark Zuckerberg lives.

Tim Redmond, a veteran Mission resident and former editor of The San Francisco Bay Guardian, sits in a café, grumbling as the Google buses come and go outside. “For more than a century San Francisco has been a Mecca for young people who were different in some way, who wanted to start again,” Redmond says. “Most young people arrived here poor, with enough to rent a place then get a job. We moved here and built a life from what we had and could find. The people who move in now are the same age – but they’re already stinking rich.”

In 2011, according to the US Census, the median income for a man aged 25-34 was $32,581 (£20,368). The average Silicon Valley salary was a little under $100,000. The Bay Area’s tech industry boasts 50 or more billionaires and many thousands of millionaires. Yet homelessness in the region has risen by 20 per cent in two years. This month, Twitter announced its imminent flotation on the stock market, which means there may soon be several hundred more tech millionaires in San Francisco. The firm was recently awarded a tax break to open its new headquarters in the heart of the city, mere blocks from the Tenderloin district, where a quarter of residents live beneath the poverty line.

The median monthly rent on a one-bedroom flat in the Mission is now $2,850. Between 2011 and 2012, San Francisco rents went up faster than in any other US city. As a result, the creative middle-classes are decamping in droves across the Bay to Oakland, with its thriving arts and food scenes. Rents there rocketed by 11 per cent in the same period.

Chris Tacy moved to the Mission in the early 1990s and established a tech start-up there shortly afterwards. So incensed is he by this latest wave of wealthy young tech workers that he recently moved out of the neighbourhood after 20 years. In June he blogged about the infestation of “start-up douchebags” bragging loudly about their bank accounts or their latest Google Glass app, with casual disregard for the community they were colonising. Tacy says: “I got upset because I thought, this is my industry, this is my community, and this is not OK.”

In August Peter Shih, a young tech entrepreneur from New York, published a blog post entitled “10 Things I Hate About You: San Francisco Edition”. In it he complained, among other things, about the number of “crazy homeless people” in his adopted city. After a public outcry, Shih took down the post and apologised, but he had already confirmed San Francisco’s worst fears about its most conspicuous new demographic.

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“In past eras of great industrial wealth… people tended to work until their 40s or 50s before they got really rich: the Rockefellers, the Morgans, the Vanderbilts,” Redmond says. “It’s remarkable to see so many people amassing great fortunes before they’re 30. There’s something wrong with having that much money so young – you haven’t learned how to behave.”

It is tempting to see this argument as so much media chatter: one group of relatively wealthy people complaining about the gentrifying influence of another group of slightly wealthier ones. Yet that petty conflict masks a more troubling truth about gentrification – that those on the lower rungs of the income ladder are being forced out of the city altogether.

“Who cares whether the chattering class are arguing among themselves? It has no effect on public policy,” says Peter Cohen, executive director of the San Francisco Council of Community Housing Organisations. “This rather silly and conceited debate among two sets of gentrifiers takes the conversation away from the fact that gentrification is very real, and that real people get hurt by these economic impacts. We need to break or slow down the cycle of gentrification for the benefit of folks who don’t just sit in coffee houses talking about their despair; they’re trying to survive.”

Though the city has seemingly strong tenant laws, loopholes allow owners to eject residents and redevelop buildings for sale or rent at vastly inflated prices. With the influx of new tech money, landlords have an incentive to do just that. Sure enough, evictions in San Francisco reached a 12-year high in 2013 – and those most affected are often the least privileged: working-class Latinos, the elderly, even people suffering from Aids.

San Francisco has struggled to rehouse those who lose their homes. Scott Wiener, who chairs the city’s Land Use and Development Committee, says: “The number one challenge in the city is housing affordability. It’s not surprising that when you have a growing population and don’t build new housing, you see an explosion in house prices. In the last decade we’ve added at least 50,000 new residents to San Francisco, and produced very little new housing.”

Though he doesn’t much care for the start-up douchebags, Redmond blames not individual tech workers for the current crisis, but property speculators and the lawmakers who have let them take advantage of their precious commodity: space. “If we had a major earthquake in San Francisco, the water mains all broke, and some guy showed up with a water truck and started selling water for $10 a gallon, people would be pissed,” he says. “That guy would be ridden out of town; he’d be attacked with sticks and pitchforks. But that’s what the real estate people are doing right now – and they’re getting away with it.”