Why are some neighborhoods better than others? Why are some blocks within the same neighborhood better than others?

The easy answer is economics, but on closer inspection other factors come into play. When all property owners on a block are committed to improving the block, everyone is better off. But when one property goes bad, it has an effect well beyond its physical border. Much like a disease, a bad building or bad tenant can infect an entire block or even an entire neighborhood.

This is a well understood phenomenon. Responsible private landlords, for example, usually require leases that allow eviction if their tenants break the law or engage in behavior that disrupts abutters and neighbors.

Indeed, in many troubled neighborhoods, the source of problems can be traced to a landlord that is not acting responsibly. Property owners who fail to keep up their property, who refuse to screen prospective tenants, or who tolerate illegal behavior are seen as a neighborhood scourge.

That is why the current controversy over evictions of public housing tenants is so puzzling. The most recent case involved the eviction of a white family from a South Boston housing project because some members of the family were allegedly committing hate crimes.

A response to that eviction was an allegation that somehow white families were being treated more harshly than African-American or Hispanic families. This turns out not to be the case. All available evidence indicates that evictions have been meted out without regard to race.

The real objection revolves around a notion that the sins of one's children should not be visited on the entire family.

Wrong. They should be. It's what we demand of private landlords. It's what we should demand of public landlords as well.

There is a regrettable history of public housing that has seemed to treat poor tenants as second class citizens. The design of many developments itself sends out this message, with the complexes being built like bunkers that are closed in on themselves, making access to the surrounding neighborhood difficult. Many developments have their own police force, a signal that somehow those citizens are not deserving of the same police protections afforded all other citizens.

Even worse, however, was a history of tolerating behavior in public housing developments that simply would not have been tolerated elsewhere. The predictable result was that public housing developments became havens of crime, neighborhoods where people literally feared to walk outside. Tenants in public housing who were trying to make something more of themselves were deeply hurt; surrounding neighborhoods in turn shunned the developments.

Much of that is changing, thanks to initiatives at the state and federal level. These changes in the law required a new philosophy of public housing. It used to be that public housing was regarded as a right, as an entitlement. Today it's different: public housing is seen as a privilege. If the privilege is abused, it's lost.

It's really quite simple. All residents of Boston, subsidized or not, are entitled to decent homes and decent communities. Rather than decrying the eviction of families who are tearing down our neighborhoods, we should welcome it.