I understand your concern, though I don't share it because I don't believe making drugs legal would lead to the dire consequences you predict. But let's assume those consequences did come true. Do you believe that situation is worse than what we have now?
Remember the hundreds of thousands in prison for non-violent offenses, ripping up families and leaving kids without parents. Remember the hundreds or thousands killed each year in the drug war violence, many of them innocent bystanders. Remember the erosion of Constitutional rights as the 4th Amendment becomes practically meaningless.
I'm not trying to bait you. I just want to know if you really think all those things are preferable to increased drug usage - hypothetical increased usage at that.
I'd put it this way. I like the state I live in, but if it decided to legalize all drugs, I would be out of here faster than you can say epidemic.