It's because they're thinking.
"HUUUUUUUUURRRRRR, ITS ONLY AN IMMENSELY POWERFUL DRUG I SHOULD BE ABLE TO TAKE IT WITHOUT CAUSE OR CONSEQUENCE. ITS MY RIGHT DO EAT/SMOKE/INJECT WHAT I WANT. OTHER WISE THE GOVERNMENT IS TAKING AWAY MY RIGHTS. HUUUUUUUUUURRRRRRRRR"
No, it's not your ****ing right. Things are illegal for a reason.
Yeah, because it's impossible for a drug user to think about the negative consequences from the use of a highly psychedelic drug. Give "druggies" some credit, will you? Everyone does things for different reasons, and it doesn't make sense to generalize and incredibly large number of people like that.
As for my stance on this issue; I think all drugs should be legal. People should have the right to make decisions own. If the government really wanted drug use to decline, they'd give people the FACTS about drugs, instead of hiding the truth with propaganda and trying to scare the common public into thinking drugs are dangerous. That's not to say a lot of drugs aren't dangerous, but if people knew what they were putting in their body, than they can be responsible for the negative consequences.
Whether or not drugs are illegal, people are always going to do them, and throwing a bunch of druggies in jail isn't going to solve anything.