I agree that the war on drugs is stupid and causes more harm than good. However, the counter argument that "people should be allowed to do things that only hurts themselves" is pretty poor in the case of most addictions (including but definitely not limited to drugs). Personally, I think people should be allowed to do whatever they want as long as there's no adverse affects to those around them. Unfortunately, most people only think of the immediate physical effects (e.g. secondhand smoke) and don't think of the more long-term effects, especially those which are harder to quantify.
If you just make it broad and vague enough practically everything will have some adverse effect on something. Or if not with certainty then with for some of the people some of the time and the increased risk meaning an increased risk. Or it's not by itself harmful but is somehow a gateway or stepping stone to something which might have adverse effects.
For example, take alcohol and let's forget all the health effects. Alcohol drinking is probably the leading cause of public urination which is clearly some form of adverse effect. It's also known that it lowers the inhibitions to violence in some people, so in the wrong situation it can clearly lead to adverse consequences. And obviously drinking is a prerequisite to drunk driving, which we all agree is bad so it's a gateway to adverse consequences. If you start putting enough bullshit like that together you can make almost anything seem bad. And I just wanted a beer.
If you preemtively need to take everyone's freedom away to avoid the risk that they'll someone infringe on someone else's freedom you're throwing the baby out with the bathwater. If I want to get drunk, I should be able to get drunk. If I'm becoming drunk and disorderly, drunk and violent or drunk and driving then you can stop me. And even assuming I've got an addiction and is borderline alcoholic, what good does being a borderline alcoholic and a criminal help me? No, I disagree with you it's my life and my right to fuck it up. If I want to go to McD and supersize it every day until I'm 500 pounds and die from obesity that should be my choice.
As for covering the costs of public healthcare, well I'd rather pay it rather than have the health nazi police trying to measure how healthy I'm living and metering out an appropriate tax/insurance premium. A truly "fair" distribution of costs would also involve a truly invasive surveillance society where I couldn't enjoy the pleasure of drinking my own beer in my own house without somebody recording it and adjusting my risk profile. But hey, I'm willing to put that to a vote if you are...