According to the government, cannabis (Schedule 1) is more dangerous than cocaine or morphine (Schedule 2).
In this article I won't go into whether or not marijuana is good or bad for you (although every honest study done on the plant has suggested that it is generally harmless and even possibly beneficial), or just how much of an outstanding failure the drug war really is, the decimating impact the drug war has on poorer communities, or even the amount of people that die each year in Mexico from violent cartels; cartels that depend on the illegal drug trade (over 50,000 dead in the past 6 years).
I'll only talk about how prohibition is an attack on personal liberty, and therefore immoral.
The idea that the government can, and should, use force to prevent people from engaging in a non-violent, victimless act that infringes on no one else's rights (as opposed to murder, theft, kidnapping, trespassing, etc.), is nothing short of fascism. You and I have a right to life, liberty and the pursuit of happiness within the limits created by our neighbors' expression of those same rights. Therefore things like theft, murder, etc. are crimes.
But a person using or selling heroin doesn't infringe on anyone's else's rights as long as it's done peacefully. Even if you disagree with their choices, to turn them into criminals would be an assault on their rightful freedoms.
Next, the absurd idea that it's the government's responsibility to protect us from our own bad decisions. This tragic notion (responsible in part for the Drug War, gun control, and even the recent NYC beverage size limits) has somehow convinced some people that it's okay for the government for punish people for their unpopular lifestyles or decisions. The government has no authority to turn a vice into a crime. Instead, it regularly turns around and says we're too stupid to make our own decision on the matter.
Drug abuse is something that is best addressed at the immediate level (individual, family, friends, communities, church, etc.), not a reason to create militarized police forces, national bureaucracies, and a police-surveillance state. Really, the only way for the government to effectively carry out its drug war is to strip its people of their rights. Speaking of which...
The 4th Amendment:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized."
But let's not pretend that we still do anything with the Constitution other than pay it lip service. Now, if you get pulled over, a cop can say he "smells marijuana" and automatically have enough probable cause to search your car. Every email or text message you send, or phone conversation you have (some 1.7 billion messages per day) is scanned and put in a database by the NSA without need for a warrant. We now have unmanned police drones and military-style helicopters scanning our homes with infrared from above to see unusual heat signatures. A SWAT team can knocked your door down, stick assault rifles in your family's faces, arrest you and your spouse, seize the property, and send the kids to a foster home just because you grew a certain plant in your house.
The Drug War has established a surveillance system that does not exclude innocent people. It has eroded our personal liberties and and given the government the power to punish people for their lifestyle choices. But luckily, the current trend of nullification - that is, several states (like WA and CO) passing laws to ignore unconstitutional Federal laws - is a reason to be greatly optimistic that the government's war against its own people may soon come to an end; but dealing with the remnants of the surveillance state will be yet another battle.