Why does the government not want you to get high?

It seems to me that the government are just against people getting high, regardless of how little negative effect the drug has on health. I know that some drugs are dangerous, as there is strong evidence for it. However other drugs (cannabis, for example) show very little detrimental health effects if used properly, indeed cannabis has been shown to be beneficial to many people suffering a variety of illnesses. However the government in this country appears to claim that the act of getting high in itself can possibly damage mental health when used by individuals with underlying mental health issues. The same can be said of salvia divinorum, which is often vilified due to its potency, which is propagated to be more dangerous because of it. Salvia has only been linked to one death, a suicide, he was undoubtedly under the influence of salvia, but then again he was not using it safely and abusing it (where was his sitter?).