Mandatory minimum sentences have fundamental flaws at a lot of levels, beginning with the federal government overreach. For example, being charged with illegal drug usage or distribution in which no action crossed state lines should logically be handled by the state involved, but in fact, many drug charges are federal crimes because the perpetrator arrested was arrested by the Drug Enforcement Agency, or perhaps was arrested on federal property, such as a national park, or simply the fact that both federal and state governments have laws governing drug usage in which either entity can bring charges against the accused.
Mandatory minimum sentences especially for drug related crimes, are often far more draconian if the accused is charged under federal law, because of the "war on drugs" and federal government laws which are highly punitive and harsh, and seemingly do not take into account exigencies, practicalities, and sensibilities of each particular case. The main reason that our federal and state governments have mandatory minimums in place for so many different crimes, is never to serve justice, never to be fair or to show true impartiality, but simply to take certain undesirables, certain oppressed peoples, and to crush them, to forget about them, and to remove them from open society.
While a significant portion of the population supports being harsh on crime, most people are completely ignorant of the mandatory minimum assigned to various crimes, and few understand or comprehend the costs to society, and to the individuals involved that are inflicted by our mandatory minimum sentences. However, there are definite segments of our society that benefit from mandatory minimum sentences, which includes our court system, our police, and the prisons themselves, in which each of these components either receive more money by virtue of having more criminals or receive more services and infrastructure provided to them to support the incarceration of miscreants or all of these things.
There isn't any doubt that mandatory minimum sentences have very little to do with justice, or fairness, or in reforming of the criminals that are incarcerated for their crimes. A policy in which we simply lock up people that don't conform to arbitrary rules and laws, or additionally are possibly an embarrassment or an inconvenience to society at large is a policy which is wholly misdirected.
There are some criminals that are a menace to society, that are a danger to our citizens, and probably rightly should be incarcerated or restrained in their freedom of movement, such as murderers and rapists. There are also a massive class of criminals that have committed no crime, because there isn't a real victim, such as drug users, or prostitution and small-time drug dealers that are essentially providing a product to a willing consumer.
It has been said, that idle hands are the devil's tool, and this is a fact that has been played out in America time and time again, in which whole sections of certain communities have no viable income or opportunity, little education, and little hope. People that turn to "crime" in these types of situations are often expressing their hopelessness in which their cry is for help, for comfort, and for good will. Our response to these people is the true measure of our country, and of our justice, which is too often to lock them up and to lie to ourselves that they don't exist, that they are meaningless, that they are not us.