America has all sorts of laws against unauthorized drug possession, against drug usage, and against drug sales, of which, certain drugs are listed unto the restricted federal schedule, in which, those drugs are thereupon categorized into their particular degree of harm to those that use them, in conjunction with their degree of abuse or addiction perceived, per drug. Whether those drugs are properly categorized is subject to debate; nevertheless, the penalties for those that have possession or usage or sale of these drugs are coordinated with the partition of these drugs per that schedule.
The FBI's uniform crime report for 2017, states that there were 1.63 million arrests for drug law violations, of which just over 1.4 million, were just for drug possession. This means that approximately 85% of the drug arrests performed in this country had nothing to do with the illegal distribution of drugs, or the actual usage of the illegal drugs, or even the manufacture of illegal drugs, but actually occurred for the simple possession of those drugs. Further to the point, in order to be arrested for the possession of drugs, means, in most cases, that the person so being arrested was stopped in the street, such as in "stop and frisk"; or stopped while driving their vehicle, for whatever reason, dubious or not; or were found to have illicit drugs inside their place of abode. In all of these cases, the person that has been arrested for drug possession, has been arrested basically because they are not secure in their persons, as per their Fourth Amendment rights, but have had that security breached, by law enforcement, rightly or wrongly.
Additionally, according to drugabuse.gov, "in 2013, an estimated 24.6 million Americans aged 12 or older—9.4 percent of the population—had used an illicit drug in the past month." So that it can be said, that when there are an unfathomable amount of people using an illicit drug on a monthly basis; whereas the arrests for the entire year of all illicit drug violations, is only 1.63 million, than quite obviously, a valid argument could be made that the law enforcing arm of the state, could easily arrest far more people than it already does, but clearly does not. The apparent reason why this is so, is that though law enforcement officers are very adept at arresting people during traffic stops, citizen stops, and via the visiting of citizens at home, they also are evidently very selective in those that they do so arrest, noticeably preferring to arrest those that are marginalized, impoverished, ill-educated, and poor.
In other words, law enforcement deliberately does not concentrate upon those that are engaging in illegal drug usage and possession at, for instance, our higher institutions of learning, nor does law enforcement concentrate on arresting for illicit drug possession those that live or congregate in very nice areas, or things of this sort; though illicit drug possession and usage, is rather common throughout all segments of America, but rather, law enforcement is quite cognizant of the fact that arresting the wrong people, has negative consequences for all those in that industry. That is to say, the laws so written for illicit drug usage, are broad enough, to arrest far more than the 1.63 million arrests yearly, but are selectively enforced primarily upon those that are the underclass of America; as well as being held as a valued weapon in the state's arsenal to be deployed against all those that are considered to be annoyances or enemies of the state, now or in the future.