Personal interest is what motivates us (alone or within a group) to act, be it to improve our lives or afterlives. This personal interest can sometimes be detrimental to others, and even violate their person or property. It is especially obvious in the War on Drugs, where police forces act in more than questionable ways to secure more funding.
But police officers are far from being the only group that profits from the prohibition of marijuana and lobby to keep it that way — many law enforcement groups in California lobbied against AB 684, which would have legalized hemp culture in the Golden State. Also, as much as 30% of law enforcement revolves around pot prohibition.
Political powers at all level profit from it. Since they like expanding, they have creatednumerous agencies (like the DEA and FDA) and programs (like DARE) to give jobs to their friends and keep pot illegal. And in order to do so, they often distort facts and science. In the 1930s, when pressure was mounting to make pot illegal, Fiorello La Guardia, mayor of New York City, commissioned a team of scientists to see if the sensationalist headlines about pot were true, and they weren't: it didn't lead to stronger drugs, it wasn't causing crime and the fears of its catastrophic effects on society were unfounded.
Unhappy to see that the facts didn't support his conclusions, Harry Anslinger, first head of the Bureau of Narcotics, questioned the credibility of the study. His bureau produced a study with the wanted conclusion (that pot is dangerous) by blackmailing the American Medical Association. All these factors, combined with a biased Indian Study that found a link between marijuana and crime, helped keep pot illegal since 1937.
In the 1960s, more studies showed what the La Guardia study showed, i.e. the negative hype around pot was unfounded. The anti-cannabis law was even struck down as unconstitutional in Leary v. United States in 1969. So obviously, Congress did what it had to do ... and kept pot illegal with the Controlled Substances Act of 1970. And since pot was becoming popular again, the government funded other “studies,” such as the infamous Tulane Project to show the harm of pot on the body. They made a rhesus monkey inhale the smoke of 90 to100 joints daily — even the biggest tobacco smokers don't smoke nearly as much. They also put the smoke through an oxygen mask so the monkey would inhale it all. It was then concluded that pot kills brain cells.
As late as 2008, the DEA was still stating that pot was a gateway drug — that it eventually leads to using stronger drugs like heroin and cocaine — even though no serious study has ever shown this to be the case.
The next time your hear politicians claim they have your interest at heart when they support drug prohibition, don't be fooled. They only care about themselves and being elected, and being "tough" on drugs and crime can be a part of this. As long as they can be elected by waging the War on Drugs, they will.