prison sentence

There are simple enough reasons for prisoners being incarcerated, because they were obviously committing an illegal activity. Are the sentences fair for the crimes committed? Drug dealers get 5-10 yrs. for the sales of cocaine, marijuana, and heroine. Pedophiles do shorter times depending on the severity of their lewd act committed upon a child. A drug dealer sells to a person who is aware of their problem and who makes their own decision, whereas a pedophile takes advantage of children who cannot give their consent. Society has their principles all wrong and therefore I question when and why prisoners should be released for a crime that has taken place?