It is true and it is relevant.
The reason the vast majority of people don't do recreational drugs is because they are harmful. A tiny minority abstain because they are illegal.
If you're going to cite the cost of the WOD, then it's very relevant to also point out the savings of the WOD.
The savings are already set forth and compounding. The WOD drains away from that. I pointed out some of the lost opportunity costs (lost savings) from the WOD in post 182. You assert that the set amount of savings is due to people not doing drugs. There may be a correlation but certainly not a causation. Again, that is not being honest. You cite none of the savings caused by the WOD.
Perhaps you mean when a drug dealer is arrested it stops him from being on the street where he may kill an innocent person -- saving the person's life means they can continue producing, saving and injecting capital back into the market -- that happens to be in the middle of a drug-turf battle, gun-fight. A turf war that wouldn't exist if not for drug prohibition facilitating a black market for illicit drugs with 1000% profits to be made. Take one drug dealer of the streets and it's a job opportunity for ten other wana-be drug dealers to step in and take his place.
I'm saying the WOD, all aspects of it -- interdiction, enforcement, education, advertising, etc. -- keep people off drugs. It either keeps them from starting or "encourages" them to quit.
Without the WOD, I'm saying that we would have a 50% increase (at a minimum) in the number of users. That's 10 million additional people on drugs. Keeping them off drugs represents a savings in overall economic productivity, savings in medical expenses, savings in insurance costs (for everyone), less drug-associated crime and those costs, etc.