These laws are a product of a very toxic combination of factors. Unfortunately, I think these factors are especially prevalent in the United States, though they also exist elsewhere.

The first ingredient is intensely sympathetic and aggrieved victims. Mothers who have lost children to drunk drivers or sex predators, are not a group anyone wants to ignore. Not just for political reasons, but because we (society, politicians) really are profoundly disturbed by the crimes and want to bring justice and do something about it.

The second is a bad set of laws that don't protect the innocent (at first) Laws that allow a convicted child rapist to live in a neighborhood without notifying the neighbors, laws that allow a guy who makes a habit of drinking 15 beers and driving home to say "sorry, I didn't mean to cause that horrifying accident". These things motivate society to form and back up organizations that lobby for strict laws.

The third is "lobbying as therapy." When you lose a child, you are so full of grief, and for many, fighting against the wicked is the only way to get over the grief. The problem is, what do you do when the basic legislation that should have always been there is put into place? When drunk driving is illegal and punished. When genuine, dangerous sex offenders are identified and barred from activities where they would come into contact with potential victims?

This leads to the fourth ingredient: the inertia of organizations. Interestingly, when organizations achieve their goals, they don't go away. They set new goals. Got the BAC illegal at 12%? Go for 10%. 10%? Go for 8%. Raise the drinking age to 21. Raise the jail time from one week to two. Eventually, the good and righteous work (and I'm not being sarcastic here, the early work on drunk driving and sex offenders was absolutely the right thing to do) is gone, but the organizations have funding, positions to fill, calls to make. They don't just go away.

The fifth ingredient - and this is more endemic to the US, I think - is a puritanical society that has always secretly hoped to criminalize certain types of "immoral" behavior. Prohibition didn't work, but there are still a lot of Americans who, for whatever reason, want to criminalize the demon rum. Drunk driving laws are an outlet for them. Many US states still have enforced laws that make selling a vibrator illegal (seriously). Sex offender laws may be an outlet for these folks. The problem is the same as above - what do you do when the good laws are now in place? You go for laws that are stricter, and stricter, and stricter...

Until it becomes counter productive, which is especially tragic. There's an article on SF gate today about a 29 year old woman who was abducted when she was 11 years old. She was kept in a compound by a convicted sex offender, the kind nobody, and I mean nobody, would ever defend, the kind who should without question be on these lists.

The police went to his house. He was on the registry. They just didn't find the girl for 18 years. The laws didn't protect her at all.

This is the only hope for reasonable laws - when we can explain how diverting resources to monitoring someone who peed against a wall is the same as diverting them away from monitoring the truly evil and dangerous. It's a hard sell, though. People understand how getting strict on crime can reduce it, but it's harder to connect with how being more lenient on minor offenses can, in some cases, reduce really serious crime.

The human tragedy of some of these stories is pretty serious too, and may some day help unravel the mess this has created.