Megan's law requires convicted sex offenders to register when they move into a neighborhood after serving time in prison, and gives the public access to that information. Encouraged by the federal government, all 50 states have some version of it.
Like many of our laws, it was born in outrage.
California's "Three Strikes and You're Out" law was passed by state voters who were sickened by the 1993 kidnapping of 12-year-old Polly Klaas by a repeat offender who should have been kept in prison.
The first Megan's law was enacted in New Jersey and named for 7-year-old Megan Kanka, who was sexually assaulted and killed in 1994 by a repeat sexual offender.
But what the public demands in outrage the Supreme Court is supposed to review in the cold light of reason and law.
The question for the justices will be twofold:
Does Megan's law punish someone twice for the same offense? The Constitution prohibits double jeopardy or the increase of punishment after the fact.
And do the states have to prove that sex offenders, some of whom have been convicted of non-violent offenses, are dangerous before they are added to a public list?
A look at 1997's Kansas vs. Hendricks may give us an idea of how the Supreme Court may approach the Megan's law case.
In Hendricks, the Supreme Court upheld Kansas's Sexually Violent Predator Act, despite doubts by a significant minority of the justices.
The act allowed the state to use civil commitment to confine sexually dangerous prisoners after even they had served their time in prison.
Inmate Leroy Hendricks agreed with a state physician that testified at his trial -- he was a habitual child molester, and he would continue to molest children even after he was released.
Nevertheless, Hendricks challenged his commitment, and the state courts agreed that his right to due process, or a fair proceeding, was violated.
At the Supreme Court, a 5-4 opinion written by Justice Clarence Thomas reversed the state courts and upheld the act.
A state judge determined that Hendricks was dangerous before he was committed, Thomas said. Moreover, his commitment was a civil proceeding, while his trial was a criminal one. There was no double jeopardy, the justice reasoned.
The court's liberal wing, led by Justice Stephen Breyer, was troubled enough to dissent.
Kansas conceded that Hendricks's condition was treatable, yet it didn't treat him in prison, and it treated him only marginally in civil commitment Breyer said.
That fact, and others, "convince me that it was not simply an effort to commit Hendricks civilly, but rather an effort to inflict further punishment upon him."
Wednesday's case in the Supreme Court deals specifically with Megan's law in Connecticut, though an eventual decision will affect such laws across the country.
A federal judge and then a federal appeals court ruled that the Connecticut law is unconstitutional because it punished an offender with a law that was not in effect when the crime was committed.
It's doubtful that the Supreme Court will agree. The justices will look at the express purpose of the law -- making neighborhoods safer -- and will probably come to the conclusion that the law is constitutional. The vote may not even be close.
So why did we have to go through this extensive process, putting the law in jeopardy?
It's better this way. We pass laws in anger, in the heat of our outrage. The courts, ultimately the Supreme Court, are an important check on our emotions.