Criminologist: Some legislators advocate mandating a sentence of life in prison for anyone who, having twice served sentences for serious crimes, is subsequently convicted of a third serious crime  These legislators argue that <b> such a policy would reduce crime dramatically </b>, since it would take people with a proven tendency to commit crimes off the streets permanently  What this reasoning overlooks, however, is that people old enough to have served two prison sentences for serious crimes rarely commit more than one subsequent crime
<b> Filling our prisons with such individuals would have exactly the opposite of the desired effect, </b> since it would limit our ability to incarcerate younger criminals, who commit a far greater proportion of serious crimes
The first is a conclusion that the argument as a whole seeks to refute; the second is the main conclusion of the argument.