Judging how many years a criminal should be in prison is the duty of the judge not ours.
Every member of a society should respect and obey rules. If someone hurts others’ physical health or feelings, he or she should be punished according to the law. However, all men are equal in the sight of law. The law is the only criterion to decide whether a man should set to free.
As far as I can see, reducing the crime rate is likely need more than a sample prolonging the term of imprisonment. There are various measures that could be implemented that would have a huge impact on these problem.