I believe that mandatory sentencing does counter judicial discretion and I do not think that is a good thing. Judges are elected or appointed officials with lots of experience. A judge may make a better decision based on circumstances and evidence than by just following a law that mandates a minimum or maximum amount of sentencing. Additionally, it has been proven that some mandatory sentencing laws are discriminatory.
Mandatory sentencing is a terrible thing. When a particular sentence is
mandated, a judge cannot shorten it, or offer probation or parole, even
if there are obvious extenuating circumstances. He or she also cannot
generally extend a sentence beyond statutory limits, even if the crime
was perpetrated in a particularly violent or damaging way. Mandatory
sentencing does not let judges do their jobs.
Judicial discretion can be a good thing most of the time, however, mandatory sentencing can ensure equality across the judicial system. Without mandatory sentencing judges in one part of the country may not hand down similar sentences as another judge in a different county, city, or state. Mandatory sentencing allows there to be a general guideline on what is appropriate across the country.