Victor Davis Hanson pointed out some years ago that California ignored its premodern problems while dreaming of postmodern marvels such as high-speed rail. There’s no better example of a premodern problem that’s been allowed to take root and thrive than the Medieval diseases now plaguing the state.

California Healthline recently reported a resurgence in infectious diseases, some of which “ravaged populations in the Middle Ages.” Downtown Los Angeles, for instance, has a typhus problem that “briefly closed part of City Hall after reporting that rodents had invaded the building.”

While “epidemic typhus was responsible for millions of deaths in previous centuries, it is now considered a rare disease,” says the Centers for Disease Control. Yet last year there were 124 new cases reported — a record — in Los Angeles, according to the California Department of Public Health. There were 20 cases in Pasadena, “well above the expected one to five cases per year,” says the city’s health department, and 12 in Long Beach, twice the usual number found there.

At the same time, Hepatitis A, which is spread primarily through fecal matter, has “infected more than 1,000 people in Southern California in the past two years,” says California Healthline.

Hardest hit are the homeless. But the hazards are not limited to only the homeless population. As Gov. Gavin Newsom has said, the state’s homelessness crisis “is increasingly becoming a public health crisis” that threatens residents, businesses, workers, and tourists.

California has arrived in a modern Medieval era because too many live as if they are still in the Middle Ages. The waves of homeless — California has 25 percent to 30 percent of the nation’s homeless though it makes up only 12 percent of the U.S. population — are creating the outbreaks by leaving trash and human waste on the streets, sidewalks, and other open public spaces. “Parts of this shining city,” says one observer, have become “a menacing and grimy environment.”

It is not unreasonable to expect the homeless to pick up after themselves, and to practice healthy hygiene. Or to be punished for littering, and defecating and urinating in public. But there is a “homeless-industrial complex” that has allowed, and possibly encouraged, these behaviors to get out of hand. Homeless “advocates” protect those on the streets as if they are an endangered species, the sidewalks and tent cities their natural habitats, from which they cannot be removed.

Consequently, heaping deposits of trash and human waste have become so common, particularly in San Francisco, that the jails are not big enough hold every violator.

Attitudes must change, starting not with policymakers but residents who value the quality of their lives, and the lives of the homeless, over a feel-good activism and a “tolerant” permissiveness.

This isn’t to say public policy changes can’t help. Much of California’s homelessness crisis is due to the lack of available housing. State and local governments need to remove the barriers to homebuilding they have erected over the decades. One idea is Gov. Gavin Newsom’s State of the State proposal to expedite judicial review of California Environmental Quality Act challenges to speed up construction of new housing.

But then this takes us back to private initiatives. Rather than oppose construction of new homes, residents should embrace it and encourage their elected representatives to pursue market rather than political responses. California needs fewer NIMBYs (not in my backyard), which it is overflowing with, and more YIMBYs (yes in my backyard).

There is even an organized growing YIMBY movement in the state. While it has been criticized as “techies hawking free market ‘solutions’ to the nation’s housing crisis” and ridiculed for its “nontrivial links to conservative libertarian groups” whose leadership “embodies a conservative agenda of promoting state deregulation over local control, along with a focus on property rights,” at least someone is promoting private-sector remedies.

YIMBYs have been involved in heated exchanges with tenant groups and those protecting the status quo, so they must be careful. They don’t need to confront NIMBYs as much as politely persuade them.

Though they’re unlikely to ever admit it, NIMBYs are a big part of the problem. They oppose new housing, especially shelters, group homes, and multi-family units because they believe those developments will increase litter and crime in their neighborhoods.

But those issues, as well as diseases the modern world had virtually eradicated, have already arrived in many tony neighborhoods, as homelessness threatens to swamp communities that at one time were sheltered in protective bubbles. Tomorrow’s YIMBY’s are yesterday’s NIMBYs mugged by today’s reality.

Kerry Jackson is a fellow with the Center for California Reform at the Pacific Research Institute, a nonprofit group advocating for limited government.

The views and opinions expressed in this commentary are those of the author and do not reflect the official position of The Daily Caller.