Live in San Francisco long enough, or all your life, and certain conversational bits get so stale they become rituals: That Mark Twain quote about summer. The whining about Muni. And can you believe how much they’re charging for X?

The price of food is always higher than we think it should be. Yet, in a time when menu prices are going up so quickly that we notice them from one visit to the next, complaints about food costs are taking on an urgency that echoes, and stems from, our horror over housing prices. Yelp and social media have made millions of barstool gripes about food prices public, for better and for worse, and restaurateurs are being forced to defend themselves publicly, too.

Diners’ complaints can be as simple as a tweet that @mobidevJC posted about Deli Board, a SoMa sub shop, on May 31: “I love @deliboard, but their prices are getting ridiculous.” After another user challenged the statement, he followed it up with, “No one said anything about ripping off customers. Simply find $15 high for a simple sandwich w/ just brisket & cheese.”

Deli Board didn’t hide the comment — in fact, owner Adam Mesnick retweeted it to his followers, with the response, “San Francisco may top the list for most expensive city in the states, so at 15$ it’s a steal.”

Two days later, Amy Brown, co-owner of Marla Bakery in the Outer Richmond, made public another exchange with a onetime customer who posted a long message on the bakery’s Facebook page railing about Marla’s $8 loaves of bread and $2.50 bagels. His neighbors, the customer added, felt the same way.

“Every single person has told me the same story,” he wrote. “We tried it ONCE, & the food was good, but it was too expensive to go back unless it was a special occasion.”

The customer ended his comment: “BALBOA STREET IS STILL A MIDDLE-CLASS & FAMILY AREA & GOURMET GULCH PRICES … no matter how good the food is ... DON’T FIT THE AREA.” (Punctuation and capitalization his.)

Brown’s response was soul-searching and eloquent. “I have worked in restaurants and bakeries in this city for over 20 years,” she wrote. “I am a neighborhood local — as is almost every person that works with us at Marla Bakery. And that’s the thing. People. At Marla Bakery, we make almost everything we serve from scratch. By hand. That $2.50 bagel? Rolled by hand. Boiled and then baked by our bakers. The bread? Of which everyone but Challah is less than $8.00 (most loaves are actually $5 or less)? Mixed, shaped and baked by hand, in a wood burning oven fired every day by hand, cleaned out for baking at 3 am every morning ... by hand.

“Making food this way isn’t cheap and you are right, our prices our higher. Our ingredients cost more, our labor going into each product costs more. It will always be less expensive to buy cream cheese than to make our own farmers cheese for our bagels. It will always cost more to grind our own meat for burgers, cure our own pastrami, make our own bread than it would to buy these things pre-made, mass produced. Machines are cheaper than people. We don’t do this to seem elitist, we do this because we think what comes from people’s hands tastes better than what comes from machines.”

Yet neither complaint is baseless. According to the U.S. Department of Agriculture Economic Research Service, the cost of “food eaten away from home” in the Bay Area has risen 34.6 percent since 2006, showing a particularly steep spike since 2014 — not surprising, considering that local minimum wages and commercial rents are mounting as well. The cost of food eaten out in the Bay Area is 6.9 percent higher than the average, topped only by prices in Dallas and Seattle.

Deli Board maintains an archive of daily specials on its website, and a quick search shows the average price of a sandwich has risen from $11 to $15 in just three years. And $2.50 is a lot for a bagel compared to ones from not-completely-mechanized House of Bagels and Berkeley Bagels.

At the same time, why is the baseline price of an item always how much you pay for it at Safeway? Who objectively determines the value of a bowl of pho, a hamburger, a bagel?

One of the most refreshing elements of Brown’s response is that she describes why her food costs more without using the word “should,” which far too often infects Northern California discussions of the artisan and the sustainable: Everyone should, some say, be spending $25 for this rotisserie chicken. That $14 pint of jam at the farmers’ market is what preserves should really cost. Advocates love to defend their shoulds with the statistic that, as of 2014, Americans spend only 12.4 percent of our household expenditures on food, down from 30 percent in 1950 — omitting, just as conveniently, that according to a 2014 Harvard study, 42 percent of Bay Area residents spend more than 30 percent on housing these days, and that wages, when adjusted for inflation, have stagnated for the past 40 years.

I’d counter with my own should : Living in the second-densest city in the United States should mean that neighborhoods can support bakeries that sell $2.50 bagels and $15 brisket sandwiches — and at that same time, provide just as many food and drink options for people who can’t afford to eat $2.50 bagels and $15 brisket sandwiches.

What is wrong with special-occasion food, be it a $50 steak or $4 toast? The real problem arises when neighborhoods systematically push out restaurants that serve affordable food in favor of high-end restaurants. That displacement is currently happening on Divisadero. We’ve already seen the complete transformation of neighborhoods like Hayes Valley, in which almost every restaurant is now a destination.

I headed to Balboa Street after reading Brown’s Facebook exchange, walking up and down the strip where Marla Bakery is located. (Confession: I sometimes drive there just for a bagel, too.) I passed coffee shops both chichi and scuffed, inexpensive dumpling shops, a sports bar and grill, a red-sauce Italian place, enough bubble tea stores to sugar up several middle schools. The Outer Richmond’s mix of the moderately priced and the special is what San Franciscans should be fighting to preserve.

Jonathan Kauffman is a San Francisco Chronicle staff writer. Email: jkauffman@sfchronicle.com. Twitter: jonkauffman