David Bergland once offered Libertarianism in One Lesson . I would like to offer libertarianism in one sentence. The most succinct formulation of libertarianism I can think of is this:
Other people are not your property. In other words: They are not yours to boss around. Their lives are not yours to micromanage. The fruits of their labour are not yours to dispose of. It doesn't matter how wise or marvelous or useful it would be for other people to do whatever it is you'd like them to do. It is none of your business whether they wear their seatbelts, worship the right god, have sex with the wrong people, or engage in market transactions that irritate you. Their choices are not yours to direct. They are human beings like yourself, your equals under Natural Law. You possess no legitimate authority over them. As long as they do not themselves step over the line and start treating other people as their property, you have no moral basis for initiating violence against them ' nor for authorising anyone else to do so on your behalf. The basic principle of civilised social intercourse was stated in 1646 by Richard Overton :
To every individual in nature is given an individual property by nature not to be invaded or usurped by any. For every one, as he is himself, so he has a self-propriety, else could he not be himself; and of this no second may presume to deprive any of without manifest violation and affront to the very principles of nature and of the rules of equity and justice between man and man. .... No man has power over my rights and liberties, and I over no man's. I may be but an individual, enjoy my self and my self-propriety and may write myself no more than my self, or presume any further; if I do, I am an encroacher and an invader upon another man's right .... every man by nature being a king, priest and prophet in his own natural circuit and compass, whereof no second may partake but by deputation, commission, and free consent from him whose natural right and freedom it is.
Nor is this requirement lifted merely because you happen to be a police officer, or an elected legislator, or a member of a majority of citizens casting their votes. As Voltairine de Cleyre  pointed out in 1890:
[A] body of voters can not give into your charge any rights but their own; by no possible jugglery of logic can they delegate the exercise of any function which they themselves do not control. If any individual on earth has a right to delegate his powers to whomsoever he chooses, then every other individual has an equal right; and if each has an equal right, then none can choose an agent for another, without that other's consent. Therefore, if the power of government resides in the whole people, and out of that whole all but one elected you as their agent, you would still have no authority whatever to act for the one. The individuals composing the minority who did not appoint you have just the same rights and powers as those composing the majority who did; and if they prefer not to delegate them at all, then neither you, nor any one, has any authority whatever to coerce them into accepting you, or any one, as their agent ....
I suggest that the phrase 'Other people are not your property,' and variations thereon, might be a more useful tool of intellectual debate than some of the other slogans we more commonly use. Why not meet every new proposal to force people to do this or that with the protest 'But you don't own them,' 'But they're not your property'? At least this would reduce the issue to its essence.