"I really don't see this as the most likely scenario. Why would it follow that legalization of a drug would lead to more addicts? Cigarettes are legal and addictive and I don't smoke them"

Many people do because they are easily available in pretty much any 7-11 and gas station.

"Legal doesn't imply uncontrolled and unfettered access by all"

Then there will still be a black market and it still won't solve the issue at hand.

" the people who want to experiment with them already do so regardless of legality, health effects or cost"

Many people don't experiment because they don't know where to get them. Legalizing them also implies that they are okay (if it's legal..it has to be okay..right?)

"Sin/vice taxes already fund dozens of other things besides adult health care costs, if anything I would expect them to be exploited as a revenue generating machine that politicians could gouge for cash since it's so easy to demonize"

I would just rather not have the increase strain on our already over-taxes medical system.

Everyone that's pro-drug wants the government out of their lives, yet they are fine with increased taxes and regulations to support more and more social programs. Government taxation and regulation = control.