By Rob Davies and Julia Carrie Wong

Justin Keller, founder of a start-up business, wrote an open letter to the city mayor saying local wealthy elite should not have to endure the homeless

A San Francisco technology entrepreneur has sparked fury by labelling homeless people “riff raff” the city’s wealth elite should not have to endure.

Justin Keller, founder of start-up web business, wrote an open letter to the San Francisco mayor and police chief lamenting the sight of the city’s estimated 7,000 homeless people.

In a missive that underlined the gulf between the city’s moneyed technology entrepreneurs and its sizeable street community, Keller expressed his “concern and outrage over the increasing homeless and drug problem that the city is faced with”.

“I’ve been living in SF for over three years, and without a doubt it is the worst it has ever been,” he said.

“Every day, on my way to, and from work, I see people sprawled across the sidewalk, tent cities, human faeces, and the faces of addiction.”

“The city is becoming a shanty town … Worst of all, it is unsafe.”

Keller said he had been moved to write the letter after a visit from parents and relatives was disrupted by three encounters with homeless people.

On one occasion Keller was forced to contend with “a homeless drunken man” in the street, on another he ran into a “distraught and high” person outside a restaurant.

A third encounter involved a man who “took his shirt off and laid down” in a cinema.

Keller said he should not have to be confronted with such sights because he had worked hard and made a lot of money.

“I know people are frustrated about gentrification happening in the city, but the reality is, we live in a free market society,” he said. “The wealthy working people have earned their right to live in the city.”

Despite expressing concern about the scale of the homelessness “problem”, Keller’s letter contained little sympathy for people living on the streets.

“I shouldn’t have to worry about being accosted. I shouldn’t have to see the pain, struggle, and despair of homeless people to and from my way to work every day,” he wrote.

Keller went on to say that during the Super Bowl, American Football’s blue riband event, the “homeless and riff raff” seemed to “up and vanish”.

He later wrote an apology for use of the term “riff raff”, saying his choice of words had been “insensitive and counterproductive”.

The apology followed a flood of anger on social media sites such as Twitter, where fellow people from San Francisco and further afield lined up to condemn him. Tech recruiter Ionut Roghina wrote: “Thanks Justin Keller for reminding us how entitled privileged people feel about other human beings. Always refreshing.”

Health policy advocate Andrew Noble said: “Dear Justin Keller: so sorry you have to see poverty. Must be hard on you.”

Another Twitter user, also called Justin Keller, was forced to protest that he was not the one responsible for the “myopic” open letter.

In an email to the Guardian, Keller defended his stance and said he would write a new blog post about the issue.

“The thesis of the post was that inaction by the city and officials is not working. We all as citizens of San Francisco need to figure out how we can improve the city and address the homeless and drug addiction problem straight on,” he said.

“I in no way meant to vilify homeless or drug users, my frustration was that we as citizens don’t feel safe. The amount of violent crime is increasing, and it affects everybody. What specific measures is the city taking to proactively help the homeless and drug addicted?”

“Instead of crucifying me, we all as citizens should be crucifying the city and elected government officials for ineptness. The status quo is not working.”

But Keller’s explanation seems unlikely to attract as much attention as his original post, which met with dismay from some of the city’s homeless people.

“Being homeless is like being the germ of the city. That’s how they treat you,” said Bercé Perry, a homeless resident of San Francisco who lives in a tent under the Highway 101 overpass.

The 42-year-old, who said he had been homeless for about a year, has little patience for the distaste some people have for his presence in the city.

“They don’t care about nobody but themselves,” Perry said about the wealthy tech workers who’ve moved into San Francisco.

“If you got money, you just want to grab anything you can get.”

Michael Jones, who has been homeless for about three years, was frustrated that people are homeless and hungry in a city with so much wealth.

“I see all the food that they throw away,” Jones said.

But asked about how he feels about wealthy tech workers, he would only say, “I don’t judge anyone.”

Madeleine McCann, 27, had sharp words for any of San Francisco’s so-called “tech bros” who might disapprove of her.

McCann has been living in a tent under the highway since her van was towed, leaving her without a roof.

“They need to be a little more tolerant”, she said. “It’s not like they’re going to let us come shower at their house.”

Keller can draw on the experiences of previous “tech bros” – as its young, male entrepreneurs are known – to fall foul of the city’s famously tolerant ethos.

In 2013, start up founder Peter Shih deleted an article called 10 Things I Hate About You: San Francisco edition after a backlash that saw posters featuring his photograph posted around the city.

And fellow startup boss Greg Gopman sought to make amends for an even more unvarnished rant about the homeless than Keller’s by proposing his own program to “solve” the problem.

He had described the homeless as a “burden and liability”, “the lower part of society” and “degenerates [who] gather like hyenas”.

His proposal, which involved housing people in giant domes, did not amount to anything and was described to the Guardian by one city official as like “a dog house”.