Great example, because really - cigarette smuggling is going to be a big problem
Considering the fact that right now, high grade marijuana rivals the price of gold per ounce, the government could tax the living heck out of it - and it would still be cheaper than buying illegally grown and distributed pot. And the money would go to Uncle Sam, as opposed to some Central American drug lord.
And as to "slippery slope logic", apparently you've not been around long enough... Slippery slope logic is faulty. Look it up, it's one of the most prevalent logical fallacies. And amazingly, you've provided excellent proof of that in your own post - Abortion has been legal for 35 years now, and I've never heard any suggest that killing anyone under the age of 1 should be legal as well.
I don't personally have any use for drugs either, I have much better things to spend my money on, as well as far better ways to spend my time. However, I was a teen in the 90's - I've tried just about everything - really the only exceptions are crack, heroin and PCP. Despite all that I maintained a 3.8 gpa or above, grew up, accepted responsibilities and I'm now a productive, taxpaying member of society raising kids of my own. I was a pretty well behaved kid, no drug I ever tried changed that. No amount of intoxication or illegal experimentation changed who I was or my ideas of right and wrong, and believe me - If you've not eaten magic mushrooms or tried LSD, you've no notion of what "altered consciousness" can mean. In fact, those are the only "crimes" I've ever committed. They didn't harm me, they didn't harm society or anyone else around me.
Drugs don't ruin people, they make their own decisions. When speaking of addicts, your speaking of a type of person - if not "insert drug x here" then it would be some other substance or pattern of behavior. Drugs won't turn an otherwise good, responsible person into a worthless addled addict. Even under the influence of drugs, alcohol or what have you - people are still responsible for their own actions. I've tried no drug that disengages the conscience - If you're scum on drugs my guess is that you're scum sober too. If you're a good, productive, conscientious person to start with, drugs aren't going to change that.
Drug use already has a very negative stigma in our society, but no amount of stigmatization, legislation or wasted tax money are going to stop people from using drugs. There will ALWAYS be a market for recreational drugs, until we take control of their distribution away from the criminals, the "cure" will continue to be worse than the disease.