Yes ma'am!
Lets create a little scenario here, the USA decides that they are sick of fighting a war on drugs and so they make them alll legal. Suddenly Mr White who owns a business and does a little coke under his desk every now and again can buy his fix legally. Although coccaine is addictive, this is not that much of a problem because Mr White has a stable income from his proffitable business.
all health risks aside, Mr White is not hurting anyone, and sure he is throwing away alot of money, but he has an income to support this habbit.
Now Mr Black has a 9-5 job at Walmart. He too decides to try crack seen as it is now legal. Mr Black becomes hooked[because crack is one of the most addictive drugs] and he finds himself spending all his pay check and maxing out his credit card to support his addiction. Now Mr Black has to turn to a life of crime and robs peoples houses for the money he needs. Mrs Black turns to prostitution.
Thats basically the social breakdown from using an adictive drug because suddenly crime rates hit the roof, businesses colapse from people spending too much time on drugs, theres the driving issue[drug driving a major cause of death in Australia] And hypothetically 30yrs down the track many people are dieing at 60 from using drugs with unknown effects on brain structure.
Weed is not very phsiologically addictive, but users can become dependant on it. The main problem is a Psychological addiction where users feel they need it to be happy.
and dont let us forget about mental illness as Zoe helpfully pointed out. I dont want the taxes i have to pay doubled just because a huge group of fuckwits decided weed was good and now are being supported on my money in a mental institution. We have enough to worry about with providing pensions for the baby boomers than you very much.