Your theory about "mass incarceration" (vague term) reducing violent crime is poorly supported.
I guess you haven't read a representative sample of the research in this area. Here's a sample for the masses from Stephen Dubner's
Freakonomics:
During the first half of the twentieth century, the incidence of violent crime in the United States was, for the most part, fairly steady. But
in the early 1960s, it began to climb. In retrospect, it is clear that one of the major factors pushing this trend was a more lenient justice system. Conviction rates declined during the 1960s, and criminals who were convicted served shorter sentences. This trend was driven in part by an expansion in the rights of people accused of crimes—a long overdue expansion, some would argue. (Others would argue that the expansion went too far.) At the same time, politicians were growing increasingly softer on crime—“for fear of sounding racist,” as the economist Gary Becker has written, “since African-Americans and Hispanics commit a disproportionate share of felonies.” So if you
were the kind of person who might want to commit a crime, the incentives were lining up in your favor: a slimmer likelihood of being convicted and, if convicted, a shorter prison term. Because criminals respond to incentives as readily as anyone, the result was a surge in crime.
It took some time, and a great deal of political turmoil, but these incentives were eventually curtailed. Criminals who would have previously been set free—for drug-related offenses and parole revocation
in particular—were instead locked up. Between 1980 and 2000, there was a fifteenfold increase in the number of people sent to prison on drug charges. Many other sentences, especially for violent crime, were
lengthened. The total effect was dramatic. By 2000, more than two million people were in prison, roughly four times the number as of 1972. Fully half of that increase took place during the 1990s.
The evidence linking increased punishment with lower crime rates is very strong. Harsh prison terms have been shown to act as both deterrent (for the would-be criminal on the street) and prophylactic (for the would-be criminal who is already locked up). Logical as this may sound, some criminologists have fought the logic. A 1977 academic study called “On Behalf of a Moratorium on Prison Construction” noted that crime rates tend to be high when imprisonment rates are high, and concluded that crime would fall if imprisonment rates could only be lowered. (Fortunately, jailers did not suddenly turn loose their wards and sit back waiting for crime to fall. As the political scientist John J. DiIulio Jr. later commented, “Apparently, it takes a Ph.D. in criminology to doubt that keeping dangerous criminals incarcerated cuts crime.”)
The “Moratorium” argument rests on a fundamental confusion of correlation and causality...
There are certainly plenty of reasons to dislike the huge surge in the prison population. Not everyone is pleased that such a significant fraction of Americans, especially black Americans, live behind bars. Nor does prison even begin to address the root causes of crime, which are diverse and complex. Lastly, prison is hardly a cheap solution: it costs about $25,000 a year to keep someone incarcerated.
But if the goal here is to explain the drop in crime in the 1990s, imprisonment is certainly one of the key answers. It accounts for roughly one-third of the drop in crime.
