Murder, adultery, theft, and embezzling violate the rights of others; drug use and pornography do not, and so are not the legitimate concern of government. (Zoning and public health laws are gray areas in that they can protect individual rights but those powers can also be abused.)
The State is obligated to promote the common good, which includes the defense of individual rights. If the State is obligated to defend individual rights, rights must necessarily and logically come from a higher authority than the State. Not only that, but rights advocates claim that rights are true regardless of time or place; they are eternal. Eternal rights can only come from an eternal source: God.
Therefore, no one enjoys a God-given right to do evil (since God is goodness itself), whether or not another party agrees to it, i.e., drug use, prostitution and pornography.
(BTW, there is no such thing as a private vice)
Whether particular vices should be criminalized and/or punished is a different matter, and it's a decision which should be ordered toward the common good.
...What K.y.r. said.