On Monday, the Supreme Court declined to take on a case about how the city of Boise, Idaho, treats its homeless citizens, leaving in place a ruling that says it's unconstitutional to punish people for sleeping outdoors if the city lacks alternatives.

The justices turned away Martin v. Boise, a case where a Ninth Circuit Court of Appeals panel ruled that Boise's practice of citing homeless people for camping outdoors violated the Eighth Amendment's prohibition on cruel and unusual punishments since these people did not have alternative shelter options.

This doesn't mean that people can just choose to sleep on sidewalks and in parks if they want to, but rather that a city cannot punish homeless people for camping in public space if the city has not provided enough shelter for them. It's a ruling about shelters and housing, not an acknowledgment of some sort of right to live on public land.

The city of Boise has since changed its ordinances to state that they won't be enforced against homeless people when shelters are full. But the Supreme Court's refusal to take the case leaves big cities with large homeless populations along the West Coast (where the Ninth Circuit rules) with a clear message that they can't use the law to try to run their homeless population out of town—the only way out is to build.

That's a problem in places like Los Angeles and San Francisco, where overly meddlesome regulations and demands from the state and the cities make it very, very hard (if not impossible) for private developers to build any housing at all, let alone affordable housing for the poor. Expensive labor requirements drive up costs, and unions threaten environmental lawsuits against developers who don't contract with them. There's also the issue of homeowners who will lobby their local council members and city planners to block new housing or businesses (or turn to California's overly broad environmental law to sue them, if lobbying fails).

It's particularly telling that the Los Angeles Times describes this outcome as a "setback" for city officials in Los Angeles and elsewhere for getting rid of homeless encampments. Even though the city has committed more than $1 billion to build housing for its massive homeless population, resistance from within neighborhoods themselves have made it nearly impossible, and even where it is possible, regulatory and bureaucratic hurdles have made it absurdly expensive, approaching $700,000 a unit.

Reason TV's Zach Weissmueller recently covered L.A.'s inability to house its homeless population: