There’s a rule of thumb in California politics: When polling low or otherwise in doubt, go after the sex offenders. Perhaps this is why Gov. Arnold Schwarzenegger has thrown his support behind an Orwellian ballot initiative, expected to appear on the ballot next year, that would tag convicted offenders with satellite tracking devices.

But those who value liberty have reason to worry now. Under a law Schwarzenegger signed this year, sex offenders will be banned from living within half a mile of any school. Though perhaps commonsensical in theory, the new statutes may have devastating effects.

As mental health experts have pointed out, the law is deeply problematic: An overwhelming proportion of sex crimes occur within families, not among strangers; because offenders are unlikely to target random students, the restrictions are unnecessary and excessive.

Analyses by two papers predict that the law would make most of urban Los Angeles and Sacramento uninhabitable to convicted offenders. In effect, California has decided to relocate its undesirables to the modern equivalent of leper colonies, away from jobs that would again make them productive members of society.

If sex offenders are truly incapable of rehabilitation, they should be placed in protective custody in mental institutions — where our society sends those incapable of operating by its rules. For California, which is unwilling to bear such costs, the solution has been justice on the cheap.

For now, the law affects just 1,000 Californians. When basic rights must be sacrificed, though, it’s 1,000 too many.