That's because society itself has a vested interest in preventing individuals from acting in a way which harms other individual members of society, and the stability of our commonwealth as a whole. The term "legislating morality" is a pseudo-nomer - meaning it is a term which sounds like it is being properly used, but which yet is not. It makes it sounds like morality is being positively legislated - i.e., the evil theocrats are running around passing laws saying you have to do such and such. Instead, what we see is negative legislation - people being restrained FROM activities, not being compelled TO them. This restrain, however, is legitimate because people are NOT free to engage in behaviours which harm others. We can see this for obvious examples such as murder or robbery, but many (i.e. libertarians) miss it for other activities like drug use which, while not perhaps being as overt, are yet destructive and corrosive to the lives of individuals and the cohesiveness of our commonwealth as a whole.
"Limited government" does not mean "no government". Government is properly limited to keeping individual members of society from harming other members - i.e. an arbitrative role.
Libertarians need to learn that their bumper sticker slogans no longer have any force or value. They need to get serious about actually defending what they believe, and provide justifications for why they think we ought to allow drugs (or pornography, abortion, or whatever else you choose to name) , rather than just whining abut social conservatives being "theocrats" or "communists" (actually had some fool call me that yesterday on the porn thread!).
That's because society itself has a vested interest in preventing individuals from acting in a way which harms other individual members of society, and the stability of our commonwealth as a whole.
The problem with this is that "harm" is defined so broadly as to permit any manner of government intervention in private affairs. Free men ought be able to make choices in their lives that you or I wouldn't make, or the government would prefer we don't make.
Liberals make the same claim you do, they just have slightly different targets - that guns are inherently harmful to a civil society, etc.
We must limit the government's regulatory power to what causes others actual physical or financial harm, not mere offense or distaste.
This example, however, is where social conservatives fail, because it's impossible to believe they have the best interests of the individual in mind, in legislating against things like drugs, when relatively harmless drugs like marijuana are criminalized to the same extent as more harmful drugs like cocaine, heroin, LSD, and many others. Even more ironic is that alcohol, a very destructive drug, is perfectly legal.When the polity is led to believe that those who make the laws may not have the best interests of the polity in mind, and may, indeed, have other motivations for doing the things to do, the whole "it's for your own good" mindset that bolsters social conservatism falls like a house of cards. To make law that legislates morality, whether positively or negatively, one has to legislate from a position of moral authority. I can think of no other human organization with less of a claim to a position of moral authority than the Congress of the United States, or the legislative bodies of our several states.