I mean, you're the libertarian here. People should be generally free to do stuff, so long as it isn't damaging to society, right?
I guess I'm libertarian? I hate the stigma of the title, though.
In TAE's perfect world, everything dangerous is legal, but everyone is smart enough to avoid dangerous stuff. Cocaine is perfectly legal and available on the open market (allowing tax revenue) but no one is dumb enough to inhale/inject/whatever it is you do with cocaine. Dynamite is also legal, but no one is angry enough to buy a truckload of it and blow up a building. Prostitution is legal, but no woman is at a point where she'll sell her body for money, and no man is at a point where he's so desperately horny that he'd pay for it. Gambling is legal everywhere, but people are prudent enough to not gamble with their money. Abortion is legal, but teenage girls don't get themselves pregnant, women are not raped, and birth control is used by any and all who wish to time their children effectively.
In my impossibly utopia, all is well and all are free. But we all make smart choices and we all take care of our bodies.
Back here in reality, we hardly make any smart choices. In fact most of our choices are terrible. Drug abuse is widespread, across all cultural lines, and abortion is a cauterizing hot button issue, both for people who fight for it and for those who argue against it. People still cover themselves in explosives and run into mosques, or murder their peers at military bases, or fight holy wars against each other. Prostitution and gambling are widespread and an unprecendented cultural phenomenon.
I'd love to say "sure, legalize pot...no one will abuse it" but the fact is that a lot more people would have access to it that are weak-willed than currently do while pot is an illegal substance.
Libertarians do not argue for the deregulation of everything, ever. Or if they do they are pointlessly idealistic. Instead, libertarians argue for the absolute safe minimum amount of government intrusion or regulation, especially into areas where no intrusion and regulation is necessary. In the case of motorcyclists wearing helmets and addictive drugs, absolutely the government should be involved, because enough people in our society do not have the personal fortitude to make the right decision regarding these dangerous things for it to be open and widespread.