For a society so adept at categorizing people, we sure do have a tough time deciding when exactly young people become adults.

Consider the 21-ordinance debate, which came to a merciful end last week but not before reigniting the age-old “what makes an adult” argument.

On one side are those who argue the 18th birthday is the agreed–upon threshold of adulthood beyond which the government should treat everyone equally as full-fledged grown-ups. On the other side are those who believe that as long as the government is serving a reasonable public interest by babying young adults, then that’s no problem at all.

With respect to the drinking debate, proponents of the current drinking age often argue that because alcohol could damage a still-developing, immature brain, regulation beyond age 18 is acceptable.

But our societal concern for immature brains extends only so far. Why, for example, do we justify denying young people the right to make their own alcohol-related decisions with claims based on underdevelopment and immaturity but insist in many cases on trying minors as adults when that same underdevelopment and immaturity leads to breaking the law?

As of 2010, there were an average of 70,000 minors in jail or juvenile detention every day. In Iowa, the rate of incarceration for minors was 227 per 100,000, slightly above the national average during the same year.

According to a paper from the National Bureau of Economic Research, the incarceration of so many minors is seriously counterproductive. Their estimates found that “juvenile incarceration results in large decreases in the likelihood of high-school completion and large increases in the likelihood of adult incarceration.”

But these effects are even more pronounced in the portion of these minors that are treated as adults in the criminal-justice system. 

Nationwide, approximately 3,000 minors have been sentenced to life in prison, according to data from the Equal Justice Initiative. In Iowa, there are 16 juveniles serving time in state prisons, as The Daily Iowan reported last week.

The 1980s and 1990s, the heyday of tough-on-crime muscle-flexing, swept new laws into nearly every state allowing for freer prosecution of minors as adults. By the mid-1990s, around 10,000 minors per year were tried in the grown-up justice system.

Putting minors in adult prisons, treating them as criminals to be locked away rather than reformed, is bad for society and is a direct denial of the idea that a young brain is something to be molded by public policy. Incarceration serves only to harden kids into career criminals or, in some cases, lead them to death.

This is not to say that a particularly large portion of young offenders are tried as adults, they aren’t. But the callousness that characterizes the legal treatment of underage offenders in the adult legal system and the juvenile — consider the recent reports of cruel isolation tactics and poor education in the Iowa Juvenile Home — is indicative of the low priority we place on rehabilitation, on molding those young brains.

If our concern for developing brains were sincere, it would extend beyond crocodile tears for young binge drinkers to our most troubled, vulnerable youths.