1. "Do unto others as you would wish others do unto you" (the golden rule)
2. The only class of things you would wish someone to NOT do unto you is to cause you harm against your will. You would not wish anyone to interfere with your freedom as long as you harm no one. You would wish someone to protect you when you were too young and stupid to know what had to be done to protect yourself (though you probably disagreed with your parents on when exactly the transition from that state occurred). Government is just the collective organized action of people. Non-sentient beings don't have wishes, so the golden rule makes no prescriptions about what must be done to non-sentient beings except inasmuch as those actions cascade to affect sentient beings. Therefore it follows that a "prerequisite for governmental interference in an activity is that the activity harms a non-informed sentient being, or harms an informed sentient being without his informed consent", which is a more precise statement of
the most famous quote attributed to John Stuart Mill, aka the Harm Principle (taken in context, of course, because he stated that his principles of liberty did not apply to extremely ignorant peoples) 3. Activities which, through negative externalities, contribute towards the destruction of the whole society or environment, also contribute to harm people (present or future) without their informed consent, thus the society may take collective action to preserve itself and the environment.
4. Deliberately causing birth defects should be illegal.
The fetus will suffer from the birth defects after it attains sentience.
5. Abortion should be legal. Although the fetus left untouched might developed into a person, it never will, because it was aborted before attaining sentience. Therefore it cannot feel pain, and therefore the abortion caused no harm unless by contributing to future harm of other sentient individuals not aborted.
6. Drugs which do not impair the reason of their users should be legal. If someone chooses to harm herself by smoking tobacco or pot privately, that harms no one else (unless she's pregnant or she exposes somebody else to secondhand smoke without the other's consent).
6a. However, drugs that impair the reason of their users impair the user's ability to give his informed consent to future actions, putting him in the "non-informed/child/savage" category of the harm principle, justifying action for his own protection even if such action is against his will. Therefore drugs that impair the reason of their users may reasonably be restricted or banned.
7. Medical prices cause some people to die, therefore government regulation of such prices and industries is not prohibited by the harm principle, and is supported by the original golden rule. If you were sick and you could not pay for a doctor, you would wish someone to help you. Such help is not guaranteed except by a sovereign organization of the people, i.e. government as it ought to be. So socialized medicine follows from the golden rule.
8. To knowingly conceive a child that will have severe genetic diseases violates the golden rule because you would rather be healthy than get sickle cell anemia from your parents. Governmental restrictions on whether people with severe genetic diseases may have children would protect future people from harm that is done to them without their informed consent. Therefore such restrictions are justified.
