Prisons primarily serve two purposes: to punish one for committing a crime and the keep the law-abiding public safe from those deemed “too dangerous.”
The idea of prison as a punishment works fine and we needn’t even begin to dive into whether or not certain activities show be legal or illegal (drugs, for instance).
The problem is that we have a massive misunderstanding of who should be considered “too dangerous” to be allowed participation within society.
Take the extreme case of murder. One who commits murder is viewed as inherently evil and therefore dangerous. “Whether or not they are evil” is an unnecessary debate. Most of us all assume that because one commits murder, they are thus too dangerous to be let loose amongst us “good people.” What is not being considered, however, is the concept of *motives*.
Every action that is taken by anyone has behind it some sort of motive. When it comes to murder, motive could be a number of things (lust for blood, childhood grudge, drunk, depression, a traumatizing event, etc.).
If someone commits murder because of a circumstantial motive, then (surely) it would make far more sense to evaluate said motive and determine why this person killed. After said evaluation, one could possibly come to the conclusion (perhaps, even [likely] come to the conclusion) that the murderer is, in fact, not a danger to society as a whole and will likely not kill again.
After considering all of the above, the next step to take is to ponder what should be done with criminals which are determined to (not) be dangers to society.
Personally, I would imagine that putting them all to work on public service projects would be one idea, but it could really be a number of things.
In short, the human race is addicted to overusing prisons as punishments.
