But they do it all the time, don't they?
Taking drugs in the privacy of your own home doesn't require you to usurp the inaliable rights of another individual, through force of violence or threats.
OK. Where do you get the drugs, who supplies them? Who suffers when you are inebriated, with impaired physical and mental abilities? Answer: anyone around you suffers. Spouses, children, and total strangers are damaged by your inebriated behavior. Insurance premiums raise as health problems and accidents are caused by those impaired. You know, exactly like alcohol. Unending problems occur when people use inebriating substances.
You CAN'T commit rape or murder or theft, or kidnapping, etc etc etc, without violating the rights of another individual. It just can't be done. Thus, it's in the interest of the state to intervine in any case of rape, or murder, or any crime that usurps the rights of another individual, no matter where it occurs. It is NOT in the interest of the state to spend 10 billion dollars a year to put away some non-violent feb smoking a joint in the privacy of his own living room. Well, unless you have a cushy-Government job...
This is a good point. But there is no such thing as a totally victimless crime. No matter what you do in your own living room, you're still a link in the supply chain of criminals and those who don't care about the law. You're still impairing your mental and physical abilities. You are still a menace, more of a menace than you would be sober.