It IS chump change and is outweighed by the social costs. It's not worth it. The people were hoodwinked.
Read my lips - there is NO social cost. Yes, I know, you disagree because this one time one of your friends got addicted to pot and you have a whole bunch of studies and reports from fellow imbeciles who all think it's possible to see into the future using statistical analyses of the past but the fact is you have no fucking idea and that makes you wrong by default.
Some kids will get strung out on drugs. A tiny percentage. chump change, if you like. This is not a legitimate reason for prohibition.
Arguing not to end prohibition IS arguing FOR prohibition.
Your "logic" can equally be applied to prohibition of Alcohol, tobacco and sexual intercourse ANY of which harms more children in a week than pot does in a century. Therefore your priority MUST be to fight for the prohibition of drink, smokes and reproduction, given that pot is already illegal and, by your own admission, isn't likely to be legal any time soon.
Face it, mate, you're a fucking idiot. That's not intended as an insult. What I mean is you actually are a genuine, honest to god, fucking imbecile. You should get help. Find an organisation who can help you with simple things like going poo-poo and feeding yourself and leave complicated stuff like running countries to people with a basic grasp of reality.