In one sense, California’s housing crisis is a matter of simple math. This state was not building anywhere close to the number of homes that would be required to accommodate the addition of 300,000 residents a year over the past decade. Demand is greatly outstripping supply, and it’s only going to get worse with the anticipated population growth of 3.4 million by 2025.

So why isn’t that construction happening?

The causes are all political .

There are no inherently evil intentions in the people putting up these barriers. Californians who are fortunate enough to own a home in a comfortable community don’t want to disrupt their good life with newcomers clogging roads, overcrowding schools or overrunning their parks. They worry about the impact of property values.

Taxpayer groups don’t want to subsidize affordable housing. Politicians want to require below-market housing mandates that may or may not have any correlation with a development’s economic viability. Unions demand that any government-promoted housing must require union-level wages. Environmentalists and neighborhood groups want to reserve the right to challenge developments even if they fit within zoning guidelines. No city wants to be told how much it must contribute to the greater good of making its region or its state more affordable.

But add up each of those forces — and the clout that each brings to bear — and it’s clear to see why not enough building is getting done.

So the question arises: Do we have the collective will to change that dynamic, when it results in the nation’s highest poverty rate, our children unable to settle down near us and businesses struggling to recruit and retain workers in a transient economy?

So far, the answer has been no.

Just ask Gov. Jerry Brown, who last year pushed the not-so-radical notion that proposed residential projects that fully complied with local zoning and set aside at list 5 percent of their units for below-market sales should be put on a fast track. Opposition came from various quarters — tenant groups, environmentalists, the League of California Cities — but the true death blow came from the construction trades, which the Legislature’s Democrats dare not cross. Their beef: They wanted any projects that got special treatment to be subject to the equivalent of union wages.

A “prevailing wage” clause is no small deal in construction. A 2005 UC Berkeley study found that such clauses added as much as 37 percent to the price of a unit. It concluded that such union-friendly pacts essentially subsidized construction workers at the expense of low-income buyers. Those requirements work in pricey San Francisco and parts of Los Angeles, but they make projects unattainable most everywhere else.

Brown’s “by-right” plan to streamline housing died last year.

Freshman state Sen. Scott Wiener, D-San Francisco, has come in with a scaled-down plan (SB35) to spur housing construction. It would put the first real teeth in a state process that identifies how much housing each city must provide at each income bracket: Those that are out of compliance would be forced to give fast-track approval to projects that fit their zoning rules.

Asked where he is getting opposition, Wiener said, “You get pushback from everyone.” He has tried to fend off union opposition — at the expense of home buyers — by including a prevailing wage provision.

So it goes in California.

The Legislature also is looking for ways to raise money to subsidize affordable housing, though that is a futile chase:. At an average subsidy of $300,000 a unit statewide — much more in the coastal areas — it would take tens of billions to even come close to meeting the demand. Another fallacy, especially prevalent among San Francisco progressives: The focus should be limited to affordable housing. This crisis is the result of shortages at all price levels.

Gabriel Metcalf, CEO of SPUR, a San Francisco urban planning think tank, said he is struck by the “self righteousness that good liberal Democrats can have” in stopping new housing — and their failure to see the contradiction with their expressed concern for the underclass. “There needs to be a call to (homeowners’) moral conscience to care about other people who do need housing,” he said.

We all need to compromise to preserve the California Dream.

That awakening needs to reach the state Capitol, and city halls everywhere.

John Diaz is The San Francisco Chronicle’s editorial page editor. Email: jdiaz@fchronicle.com Twitter: @JohnDiazChron

What’s in the way? Plenty

Among the many factors why housing is so difficult to build in California:

City

resistance

Each local government is required to create a “housing element” that spells out how it will meet the housing needs at all income levels. But those are goals, not mandates, and many cities don’t bother to follow them.

CEQA

The California Environmental Quality Act can provide a powerful legal tool to stop development — even when the issues being raised against a project have nothing to do with environmental preservation. Competitors, unions and residents who simply don’t like a project have exploited the 45-year-old law to stop housing.

NIMBYs

An “I’ve got mine” mind-set prevails in many affluent areas that are loath to allow newcomers, especially of lesser means, to change the demographics of a neighborhood or city.

Revolving

rules

One of developers’ biggest complaints is the lack of certainty in the planning process, especially in cites such as San Francisco that give opponents multiple chances to slow or stop a project even when it adheres to all the zoning requirements. Delays can add greatly to the cost of each housing unit.

Unrealistic

targets

When politics, not data, drives a city’s affordable housing requirement ... the result can be that projects don’t pencil out. Exhibit A: San Francisco voted in June to double the portion of below-market housing to 25 percent in major projects, a figure the city controller later calculated to be too high.